Sensing temperature within medical devices

ABSTRACT

Devices, systems, and techniques for monitoring the temperature of a device used to charge a rechargeable power source are disclosed. Implantable medical devices may include a rechargeable power source that can be transcutaneously charged. The temperature of an external charging device and/or an implantable medical device may be monitored to control the temperature exposure to patient tissue. In one example, a temperature sensor may sense a temperature of a portion of a device, wherein the portion is non-thermally coupled to the temperature sensor. A processor may then control charging of the rechargeable power source based on the sensed temperature.

This application is a continuation application of U.S. patentapplication Ser. No. 13/783,761, filed Mar. 4, 2013, which claimspriority to provisionally-filed U.S. Patent Application Ser. No.61/636,304, filed Apr. 20, 2012, both of which are incorporated hereinby reference in their entirety.

TECHNICAL FIELD

The disclosure relates to medical devices and, more particularly,temperature sensors for sensing temperature of medical devices.

BACKGROUND

Implantable medical devices (IMDs) may be used to monitor a patientcondition and/or deliver therapy to the patient. In long term or chronicuses, IMDs may include a rechargeable power source (e.g., comprising oneor more capacitors or batteries) that extends the operational life ofthe medical device to weeks, months, or even years over anon-rechargeable device.

When the energy stored in the rechargeable power source has beendepleted, the patient may use an external charging device to rechargethe power source. Since the rechargeable power source is implanted inthe patient and the charging device is external to the patient, thischarging process may be referred to as transcutaneous charging. In someexamples, transcutaneous charging may be performed via inductivecoupling between a primary coil in the charging device and a secondarycoil in the IMD.

When a current is applied to the primary coil and the primary coil isaligned with the secondary coil, electrical current is induced in thesecondary coil within the patient. Circuitry associated with the IMDuses the current to charge a rechargeable power source, such as abattery, within the IMD. Therefore, the external charging device doesnot need to physically connect with the rechargeable power source forcharging to occur.

SUMMARY

In general, the disclosure is directed to devices, systems, andtechniques for monitoring the temperature of a medical device used tocharge a rechargeable power source. An implantable medical device (IMD)may include a rechargeable power source that can be transcutaneouslycharged. The IMD, an external charging device, or other medical deviceassociated with charging the rechargeable power source may include atemperature sensor for monitoring the temperature of the medical deviceduring a charging session. The temperature may be monitored to controlcharging of the rechargeable power source and/or avoid exposing patienttissue to undesirable temperatures.

The temperature sensor may be configured to sense the temperature of aportion of the device being monitored without being thermally-coupled tothis portion of the device being monitored for temperature changes. Inother words, the temperature sensor may utilize indirect temperaturemeasurement techniques to sense the temperature of a particular surfaceor material within a device.

In one aspect, the disclosure is directed to a method that includessensing, by a temperature sensor, a temperature of a portion of amedical device, wherein the portion is non-thermally coupled to thetemperature sensor, and controlling charging of a rechargeable powersource based on the sensed temperature.

Another method may comprise sensing a temperature of a portion of amedical device by a temperature sensor and controlling charging of arechargeable power source based on the sensed temperature, wherein thetemperature sensor is configured to sense the temperature of the portionwithout being thermally-coupled to the portion.

In another aspect, the disclosure is directed to a system that includesa medical device that includes a housing, a temperature sensor disposedwithin the housing and configured to sense a temperature of a portion ofthe medical device, wherein the portion is non-thermally coupled to thetemperature sensor, and a processor configured to control charging of arechargeable power source based on the sensed temperature.

The disclosure may be directed a system. The system may include amedical device comprising a housing. A temperature sensor may bedisposed within the housing and configured to sense a temperature of aportion of the medical device, wherein the temperature sensor isconfigured to be non-thermally coupled to the portion. At least oneprocessor may be configured to control charging of a rechargeable powersource based on the sensed temperature.

In another aspect, the disclosure is directed to a system that includesmeans for sensing a temperature of a portion of a medical device,wherein the portion is non-thermally coupled to the means for sensingthe temperature and means for controlling charging of a rechargeablepower source based on the sensed temperature.

In a further aspect, the disclosure is directed to a non-transitorycomputer-readable storage medium including instructions that cause atleast one processor to sense a temperature of a portion of a device,wherein the portion is non-thermally coupled to the temperature sensor,and control charging of a rechargeable power source based on the sensedtemperature.

The details of one or more example are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system thatincludes an implantable medical device (IMD) and an external chargingdevice that charges a rechargeable power source of the IMD.

FIG. 2 is a block diagram of the example IMD of FIG. 1.

FIG. 3 is a block diagram of the example external charging device ofFIG. 1.

FIGS. 4A-4C are conceptual diagrams illustrating example temperaturesensors disposed within respective IMDs.

FIGS. 5A and 5B are conceptual diagrams illustrating example temperaturesensors and structures that transfer energy associated with a desiredportion of respective IMDs.

FIG. 6 is a conceptual diagram illustrating example temperature sensorsand respective shutters for selectively sensing temperature fromdifferent portions of an IMD.

FIG. 7 is a conceptual diagram illustrating an example temperaturesensor utilizing phosphor thermometry.

FIG. 8 is a conceptual diagram illustrating an example temperaturesensor disposed within an external charging device.

FIG. 9 is a conceptual diagram illustrating an example temperaturesensor configured to detect the temperature of a phase change materialdisposed within an IMD.

FIG. 10 is a graph of example temperatures generated in a patient duringIMD recharging over a period of time using a phase change materialcartridge exchange.

FIG. 11 is a flow diagram that illustrates an example technique forcontrolling the charging of an implantable rechargeable power sourcebased on a sensed temperature.

FIG. 12 is a flow diagram that illustrates an example technique forpresenting a notification to a user for exchanging a phase changematerial cartridge.

FIG. 13 is a flow diagram that illustrates an example technique fordetecting a fault condition of a medical device component.

FIG. 14 is a flow diagram that illustrates an example technique forcalibrating a non-thermally coupled temperature sensor.

DETAILED DESCRIPTION

This disclosure is generally directed to devices, systems, andtechniques for monitoring the temperature occurring during recharge of arechargeable power source. Implantable medical devices (IMDs) may beimplanted within a patient and used to monitor a parameter of thepatient and/or deliver a therapy to the patient. To extend theoperational life of the IMD, the IMD may include a rechargeable powersource (e.g., one or more capacitors or batteries). When therechargeable power source is being recharged, the power transmitted tothe IMD may generate heat that increases the temperature of the IMD. Inaddition, an external charging device (e.g., another medical device)placed against the skin of the patient may increase in temperature whenpower is transmitted during the recharging session. This may result inheating of tissue proximate the IMD and/or proximate the externalcharging device. In order to prevent undesirable temperatures, thesystem may monitor sensed temperatures in the IMD and/or externalcharging device.

An IMD may include a temperature sensor, such as a thermocouple orthermistor, physically attached and thermally coupled to the surface ofa target component (e.g., the component of which temperature is to besensed) within the IMD. Alternatively, a thermocouple, thermistor, orother temperature sensor, may be disposed within an IMD to sense theambient temperature within the IMD. However, thermocouples directlycoupled to a desired surface (e.g., an interior surface of the IMDhousing) may be difficult and/or expensive to manufacture, and ambienttemperature sensors may not accurately measure different temperatures atspecific regions of the IMD or portions that transfer heat to thepatient.

As disclosed herein, a medical device associated with charging animplantable rechargeable power source (e.g., an IMD or an externalcharging device) may include one or more non-thermally coupledtemperature sensors. In particular, the temperature sensor is notthermally coupled, and need not be directly attached, to the portion ofthe device from which temperature is to be measured. In cases in whichthe temperature sensor is not attached to the portion of the device fromwhich the temperature is to be measured, it may be said the temperaturesensor is remotely located from that portion. The non-thermally coupledtemperature sensor may utilize indirect temperature measurementtechniques to sense and measure the temperature of locations within thedevice that are non-thermally coupled with the temperature sensor. Forexample, the temperature sensor may be an infrared (IR) temperaturesensor mounted on a printed circuit board (PCB), hybrid board, or otherlocation within the device. The temperature sensor may then be orientedto sense a temperature of a surface of a structure, component, orhousing of the medical device (e.g., the housing of the IMD or theexternal charging device) to sense the temperature at that surface. Inother examples, as alternatives to infrared sensing, the temperaturesensor may utilize phosphor thermometry or pressure measurements tosense the temperature of non-thermally coupled portions of the device.

A non-thermally coupled temperature sensor may be directed, positioned,or otherwise oriented toward a specific portion of a medical device orcomponent of the medical device to sense the temperature at thatparticular surface. Since devices may have varying temperaturesthroughout the device due to different components, materials, and/ordimensions of the device, in some examples, the device may use multipletemperature sensors to identify these different temperatures instead ofsensing a single general temperature of the device. In other examples,the medical device may include a heat pipe, light pipe, or other energytransfer element that conducts energy from a desired surface of thedevice to the location of the temperature sensor. In some examples, thedevice may include a phase change material configured to reducetemperature variations and provide a single surface for a temperaturesensor to sense the temperature. The phase change material may, in someexamples, be in physical contact with the portion of the device fromwhich temperature is desired to be sensed.

In addition to providing temperature measurements of specific locationswithin a device, non-thermally coupled temperature sensors may alsoreduce manufacturing complexity. For example, one or more temperaturesensors may be mounted to a printed circuit board or hybrid board andoriented towards the desired surface (e.g., a surface of the housing)for temperature measurement. When the housing is installed around theboard and the temperature sensors, no components need to be mounted tothe housing to achieve the desired temperature measurement. Therefore,non-thermally coupled temperature sensors may reduce assembly time,complexity, and cost.

In this manner, one or more non-thermally coupled temperature sensorsmay be used to provide temperature feedback for controlling the chargingof the implanted rechargeable power source. The IMD and/or externalcharging device may monitor one or more temperatures to control chargingand effectively limit temperatures of patient tissue adjacent the IMDand/or external charging device. For example, one or more processors mayreduce the power used during the charging session, cycle the power tocontrol heat imparted to tissue (e.g., cycle it on and off), orterminate the charging session. In another example, the processor maycommand a user interface to present a notification to the user toexchange the phase change material cartridge of the external chargingdevice when the temperature indicates the temperature controllingproperties of the cartridge have been exhausted. In other examples, thetemperature sensed by a non-thermally coupled temperature sensor may beused to perform other or additional functions. For example, a processormay compare the sensed temperature to a fault condition threshold anddisconnect the rechargeable power source from at least one electricalcircuit when the sensed temperature exceeds the fault conditionthreshold.

FIG. 1 is a conceptual diagram illustrating an example system 10 thatincludes implantable medical device (IMD) 14 and external chargingdevice 22 that charges rechargeable power source 18 of IMD 14. Althoughthe techniques described in this disclosure are generally applicable toa variety of medical devices including medical devices such as patientmonitors, electrical stimulators, or drug delivery devices, applicationof such techniques to implantable neurostimualtors will be described forpurposes of illustration. More particularly, the disclosure will referto an implantable neurostimulation system for use in spinal cordstimulation therapy, but without limitation as to other types of medicaldevices.

As shown in FIG. 1, system 10 includes an IMD 14 and external chargingdevice 22 shown in conjunction with a patient 12, who is ordinarily ahuman patient. In the example of FIG. 1, IMD 14 is an implantableelectrical stimulator that delivers neurostimulation therapy to patient12, e.g., for relief of chronic pain or other symptoms. Generally IMD 14may be a chronic electrical stimulator that remains implanted withinpatient 12 for weeks, months, or even years. In the example of FIG. 1,IMD 14 and lead 16 may be directed to delivering spinal cord stimulationtherapy. In other examples, IMD 14 may be a temporary, or trial,stimulator used to screen or evaluate the efficacy of electricalstimulation for chronic therapy. IMD 14 may be implanted in asubcutaneous tissue pocket, within one or more layers of muscle, orother internal location. IMD 14 includes rechargeable power source 18,such as a rechargeable battery, and IMD 14 is coupled to lead 16.

Electrical stimulation energy, which may be constant current or constantvoltage based pulses, for example, is delivered from IMD 14 to one ormore targeted locations within patient 12 via one or more electrodes(not shown) of lead 16. The parameters for a program that controlsdelivery of stimulation energy by IMD 14 may include informationidentifying which electrodes have been selected for delivery ofstimulation according to a stimulation program, the polarities of theselected electrodes, i.e., the electrode configuration for the program,and voltage or current amplitude, pulse rate, pulse shape, and pulsewidth of stimulation delivered by the electrodes. Electrical stimulationmay be delivered in the form of stimulation pulses or continuouswaveforms, for example.

In the example of FIG. 1, lead 16 is disposed within patient 12, e.g.,implanted within patient 12. Lead 16 tunnels through tissue of patient12 from along spinal cord 20 to a subcutaneous tissue pocket or otherinternal location where IMD 14 is disposed. Although lead 16 may be asingle lead, lead 16 may include a lead extension or other segments thatmay aid in implantation or positioning of lead 16. In addition, aproximal end of lead 16 may include a connector (not shown) thatelectrically couples to a header of IMD 14. Although only one lead 16 isshown in FIG. 1, system 10 may include two or more leads, each coupledto IMD 14 and directed to similar or different target tissue sites. Forexample, multiple leads may be disposed along spinal cord 20 or leadsmay be directed to spinal cord 20 and/or other locations within patient12.

Lead 16 may carry one or more electrodes that are placed adjacent to thetarget tissue, e.g., spinal cord 20 for spinal cord stimulation (SCS)therapy. One or more electrodes may be disposed at a distal tip of lead16 and/or at other positions at intermediate points along lead 16, forexample. Electrodes of lead 16 transfer electrical stimulation generatedby an electrical stimulation generator in IMD 14 to tissue of patient12. The electrodes may be electrode pads on a paddle lead, circular(e.g., ring) electrodes surrounding the body of the lead, conformableelectrodes, cuff electrodes, segmented electrodes, or any other type ofelectrodes capable of forming unipolar, bipolar or multipolar electrodeconfigurations for therapy. In general, ring electrodes arranged atdifferent axial positions at the distal ends of lead 16 will bedescribed for purposes of illustration.

In alternative examples, lead 16 may be configured to deliverstimulation energy generated by IMD 14 to stimulate one or more sacralnerves of patient 12, e.g., sacral nerve stimulation (SNS). SNS may beused to treat patients suffering from any number of pelvic floordisorders such as pain, urinary incontinence, fecal incontinence, sexualdysfunction, or other disorders treatable by targeting one or moresacral nerves. Lead 16 and IMD 14 may also be configured to provideother types of electrical stimulation or drug therapy (e.g., with lead16 configured as a catheter). For example, lead 16 may be configured toprovide deep brain stimulation (DBS), peripheral nerve stimulation(PNS), gastric stimulation to treat obesity or gastroparesis, tibialnerve stimulation, or other deep tissue or more superficial types ofelectrical stimulation. In other examples, lead 16 may provide one ormore sensors configured to allow IMD 14 to monitor one or moreparameters of patient 12. The one or more sensors may be provided inaddition to, or in place of, therapy delivery by lead 16.

IMD 14 delivers electrical stimulation therapy to patient 12 viaselected combinations of electrodes carried by lead 16. The targettissue for the electrical stimulation therapy may be any tissue affectedby electrical stimulation energy, which may be in the form of electricalstimulation pulses or waveforms. In some examples, the target tissueincludes nerves, smooth muscle, and skeletal muscle. In the exampleillustrated by FIG. 1, the target tissue for electrical stimulationdelivered via lead 16 is tissue proximate spinal cord 20 (e.g., one ormore target locations of the dorsal columns or one or more dorsal rootsthat branch from spinal cord 20. Lead 16 may be introduced into spinalcord 20 via any suitable region, such as the thoracic, cervical orlumbar regions. Stimulation of dorsal columns, dorsal roots, and/orperipheral nerves may, for example, prevent pain signals from travelingthrough spinal cord 20 and to the brain of the patient. Patient 12 mayperceive the interruption of pain signals as a reduction in pain and,therefore, efficacious therapy results. For treatment of otherdisorders, lead 16 may be introduced at any exterior location of patient12.

Although lead 16 is described as generally delivering or transmittingelectrical stimulation signals, lead 16 may additionally oralternatively transmit electrical signals from patient 12 to IMD 14 formonitoring. For example, IMD 14 may utilize detected nerve impulses todiagnose the condition of patient 12 or adjust the delivered stimulationtherapy. Lead 16 may thus transmit electrical signals to and frompatient 12.

A user, such as a clinician or patient 12, may interact with a userinterface of an external programmer (not shown) to program IMD 14.Programming of IMD 14 may refer generally to the generation and transferof commands, programs, or other information to control the operation ofIMD 14. For example, the external programmer may transmit programs,parameter adjustments, program selections, group selections, or otherinformation to control the operation of IMD 14, e.g., by wirelesstelemetry or wired connection.

In some cases, an external programmer may be characterized as aphysician or clinician programmer if it is primarily intended for use bya physician or clinician. In other cases, the external programmer may becharacterized as a patient programmer if it is primarily intended foruse by a patient. A patient programmer is generally accessible topatient 12 and, in many cases, may be a portable device that mayaccompany the patient throughout the patient's daily routine. Ingeneral, a physician or clinician programmer may support selection andgeneration of programs by a clinician for use by stimulator 14, whereasa patient programmer may support adjustment and selection of suchprograms by a patient during ordinary use. In other examples, externalcharging device 22 may be included with, or form part of, an externalprogrammer. In this manner, a user such as a clinician, other caregiver,or patient may program and charge IMD 14 using one device, or multipledevices.

IMD 14 may be constructed of any polymer, metal, or composite materialsufficient to house the components of IMD 14 (e.g., componentsillustrated in FIG. 2) within patient 12. In this example, IMD 14 may beconstructed with a biocompatible housing, such as titanium or stainlesssteel, or a polymeric material such as silicone or polyurethane, andsurgically implanted at a site in patient 12 near the pelvis, abdomen,or buttocks. The housing of IMD 14 may be configured to provide ahermetic seal for components, such as rechargeable power source 18. Inaddition, the housing of IMD 14 may be selected of a material thatfacilitates receiving energy to charge rechargeable power source 18.

As described herein, rechargeable power source 18 may be included withinIMD 14. However, in other examples, rechargeable power source 18 couldbe located external to a housing of IMD 14, separately protected fromfluids of patient 12, and electrically coupled to electrical componentsof IMD 14. This type of configuration of IMD 14 and rechargeable powersource 18 may provide implant location flexibility when anatomical spacefor implantable devices is minimal. In any case, rechargeable powersource 18 may provide operational electrical power to one or morecomponents of IMD 14.

Rechargeable power source 18 may include one or more capacitors,batteries, or components (e.g. chemical or electrical energy storagedevices). Example batteries may include lithium-based batteries, nickelmetal-hydride batteries, or other materials. Rechargeable power source18 is also rechargeable. In other words, rechargeable power source 18may be replenished, refilled, or otherwise capable of increasing theamount of energy stored after energy has been depleted. Rechargeablepower source 18 may be subjected to numerous discharge and rechargecycles (e.g., hundreds or even thousands of cycles) over the life ofrechargeable power source 18 in IMD 14. Rechargeable power source 18 maybe recharged when fully depleted or partially depleted.

Charging device 22 may be used to recharge rechargeable power source 18and IMD 14 when implanted in patient 12. Charging device 22 may be ahand-held device, a portable device, or a stationary charging system. Inany case, charging device 22 may include components necessary to chargerechargeable power source 18 through tissue of patient 12. For example,charging device 22 may include housing 24, charging cable 28, andcharging head 26. Housing 24 may enclose or house at least some of theoperational components of charging device 22. For example, housing 24may include a user interface, processor, memory, power source, and othercomponents. Charging cable 28 may electrically couple charging head 26to the power source within housing 24, such that charging cable 28 isconfigured to transmit power and/or information to charging head 26.Charging head 26 may include a coil (e.g., a component of charging head26) for inductive coupling or components used to transmit power fromcharging head 26 to rechargeable power source 18. In other examples,charging cable 28 and/or charging head 26 may also be contained withinor disposed on housing 24, or various ones of the components associatedwith charging device 22 may be carried by cable 28 and/or charging head26. Although a user may control the recharging process with a userinterface of charging device 22, charging device may alternatively becontrolled by another device (e.g., an external programmer).

In some examples, charging device 22 may only perform charging ofrechargeable power source 18. In other examples, charging device 22 maybe an external programmer or other device configured to performadditional functions. For example, when embodied as an externalprogrammer, charging device 22 may transmit programming commands to IMD14 in addition to charge rechargeable power source 18. In anotherexample, charging device 22 may communicate with IMD 14 to transmitand/or receive information related to the charging of rechargeable powersource 18. For example, IMD 14 may transmit information regardingtemperature of IMD 14 and/or rechargeable power source 18, receivedpower during charging, the charge level of rechargeable power source 18,charge depletion rates during use, or any other information related topower consumption and recharging of IMD 14 and rechargeable power source18.

Charging device 22 and IMD 14 may utilize any wireless power transfertechniques that are capable of recharging rechargeable power source 18of IMD 14 when IMD 14 is implanted within patient 14. In one example,system 10 may utilize inductive coupling between a coil of chargingdevice 22 (e.g., a coil within charging head 26) and a coil of IMD 14coupled to rechargeable power source 18. In inductive coupling, chargingdevice 22 is placed near implanted IMD 14 such that a primary coil ofcharging device 22 is aligned with, i.e., placed over, a secondary coilof IMD 14. Charging device 22 may then generate an electrical current inthe primary coil based on a selected power level for chargingrechargeable power source 18. As described further below, the powerlevel may be selected to control the temperature of IMD 14 and/or thecharge rate of rechargeable power source 18. When the primary andsecondary coils are aligned, the electrical current in the primary coilmay magnetically induce an electrical current in the secondary coilwithin IMD 14. Since the secondary coil is associated with andelectrically coupled to rechargeable power source 18, the inducedelectrical current may be used to increase the voltage, or charge level,of rechargeable power source 18. Although inductive coupling isgenerally described herein, any type of wireless energy transfer may beused to charge rechargeable power source 18.

During the energy transfer process that charges rechargeable powersource 18, some of the energy involved in the charging process may beconverted into heat at rechargeable power source 18, other components ofIMD 14, and/or in charging head 26, for example. When increased energylevels are used to charge rechargeable power source 18 at a higher rate,the temperature of IMD 14 and/or charging device 22 may also increase.Although the temperature of the IMD 14 housing may not achieve atemperature sufficient to burn or necrose tissue adjacent to the housingof IMD 14, elevated temperatures may be undesirable and could causediscomfort in some cases. Therefore, one or more devices may monitortemperatures of any device or component that may come into contact withor otherwise affect tissue of patient 12. The sensed temperature may beused as feedback in a closed-loop or partially closed-loop temperaturecontrol system. For example, charging device 22 may control the powerlevel, power cycle times, and/or charging time used to chargerechargeable power source 18 to reduce or minimize any undesirabletemperatures of IMD 14 that could be caused by charging rechargeablepower source 18. In addition, monitoring the temperature of IMD 14and/or the temperature of tissue adjacent to the housing of IMD 14 mayminimize patient discomfort during the charging process.

As described herein, system 10 may utilize one or more temperaturesensors to sense, measure, or otherwise detect the temperature of aportion of a device non-thermally coupled to the temperature sensor. Inone example, a temperature sensor of system 10 may sense the temperatureof a portion of a medical device (e.g., charging head 26 or IMD 14). Theportion of the medical device may be non-thermally coupled to thetemperature sensor. A processor of system 10 (e.g., a processor housedby either charging device 22 or IMD 14) may be configured to controlcharging of rechargeable power source 18 based on the sensedtemperature. In this manner, the non-thermally coupled temperaturesensor may provide feedback for controlling the charging of rechargeablepower source 18. For example, charging device 22 may control currentapplied to a primary coil within charging head 26 based on the sensedtemperature. Charging device 22 may control current, for example, bycontrolling a current amplitude, duty cycle, or other characteristic ofthe charging current. In some examples, the temperature sensor may bedisposed within a housing of the medical device (e.g., a housing ofcharging head 26, housing 24, or a housing of IMD 14). In this manner,the temperature sensor may be disposed in a medical device that iseither external to patient 12 or implanted within patient 12.

The temperature sensors (e.g., non-thermally coupled or non-contactsensors) discussed herein are generally described as non-thermallycoupled to the portion or surface of a structure to be sensed. In otherwords, the temperature sensor may not use physical contact or otherdirect measurements to sense temperature of the desired portion of themedical device. Although the temperature sensor may be physicallyconnected or mounted, through one or more members, to the portion of themedical device from which the temperature is sensed, the temperature ofthe portion is not sensed or measured through this physical connection.For example, the temperature sensor may be mounted on a hybrid board ofIMD 14, the hybrid board may be mounted to a surface of the IMD housing,and the temperature sensor may sense the temperature of a portion of theIMD housing. However, the temperature sensor may sense the temperatureof the portion of the IMD housing through a medium other than the hybridboard (e.g., through a vacuum, air, or another gas separating thetemperature sensor from the portion of the IMD housing).

Non-thermally coupled temperature sensors described herein may takedifferent forms and utilize different temperature sensing techniques. Inone example, a temperature sensor may be an infrared temperature sensor.The infrared temperature sensor may be configured to sense a level ofinfrared radiation emitted from the portion of the medical device.Generally, the intensity of the IR energy emitted from an objectincreases or decreases in proportion to its temperature. In addition,the IR energy emitted from the object may be affected by the emissivityof the material of the object. Therefore, an IR temperature sensor usedwithin system 10 may be calibrated to the specific material of theobject from which the IR energy will be detected. In any case, an IRtemperature sensor may be described as a non-thermally coupled ornon-contact temperature sensor.

In other examples, a non-thermally coupled temperature sensor mayutilize phosphor thermometry. This type of temperature sensor mayinclude an emitter component and a detector component. The emitter maybe configured to emit electromagnetic radiation toward a desiredsurface. The temperature sensor then excites, with the emittedelectromagnetic radiation, a phosphor material disposed on the portionof the object that will be measured. In other words, the object fromwhich temperature will be sensed may be coated with the phosphormaterial. A detector of the temperature sensor, in this example, may beconfigured to detect a phase shift in a luminescence emitted from thephosphor material in response to the excitation. The temperature sensormay then be configured to determine the temperature of the portion ofthe object based on the detected phase shift. In some examples, thetemperature sensor may output a signal representative of the detectedphase shift, and a processor is configured to determine the temperaturebased on the signal output from the sensor.

Non-thermally coupled temperature sensors may also utilize otherdetectable changes to determine changes in temperature of a medicaldevice. For example, a temperature sensor may measure changes topressure within the device. In a hermetically sealed medical device,changes in temperature of the device may cause a proportional change inthe internal pressure of the device. For example, an increase inpressure may indicate an increase in temperature of the device.Therefore, a temperature sensor may sense or measure changes to airpressure within the device to sense temperature changes of the device.Since pressure changes outside of the device may need to be used tocalibrate the internal pressure changes, system 10 may utilize pressuremeasurements obtained by charging device 22, for example, to correctchanges to pressure measured within a device.

The non-thermally coupled temperature sensors described herein may bemounted anywhere within the device. In one example, the temperaturesensor may be mounted to a printed circuit board within a housing of themedical device (e.g. charging head 26, housing 24, or IMD 14). From thelocation on the printed circuit board, the temperature sensor may beoriented to sense the temperature of a desired portion of the device(e.g., using infrared sensing, phosphor thermometry, or pressuresensing, as described above). In some examples, this portion to besensed may be a part of the housing, a recharge coil, or any othercomponents within the medical device (e.g., IMD 14 or external chargingdevice 22). In other examples, the temperature sensor may be mounted toa hybrid board or a separate mounting platform within the device. Inalternative examples, the temperature sensor may be mounted to thehousing of the device and oriented to sense the temperature of acomponent within the device or another non-thermally coupled portion ofthe housing.

System 10 may utilize one or more non-thermally coupled temperaturesensors in one or more medical device. For example, each of charginghead 26 and IMD 14 may include a single temperature sensor. In anotherexample, each of charging head 26 (e.g., external of patient 12) and/orIMD 14 (e.g., implanted within patient 12) may include two or moretemperature sensors. Multiple temperature sensors within the same devicemay be provided for different reasons. For example, each of the multipletemperature sensors may be oriented to sense the temperature of the sameportion of the device for redundant, backup, composite, orcross-correlated temperature measurement. If multiple non-thermallycoupled temperature sensors are used, the multiple sensors may besimilar or may instead be sensors of different types of non-thermallycoupled temperatures sensors described herein.

Alternatively, two temperature sensors may be oriented to sensetemperature of different surfaces and/or components within the samedevice. A first temperature sensor may be configured to sense a firstportion of the device and a second temperature sensor may be configuredto sense a second portion of the device. The two portions may be ofdifferent components or different areas of the same component. In oneexample, the first portion may be a one housing surface within thedevice, and the second portion may be another housing surface within thedevice. Since temperatures within a device may be non-uniform due tocomponent location, thermal transfer within the device, or otherexternal factors, the multiple temperature sensors may be used toidentify temperature variations or “hot spots” of the device. In somecases, a one or multi-dimension array of temperature sensors may beprovided to sense one or more portions of the IMD 14 or external device(e.g., recharger).

In some examples, two surfaces being sensed for temperature may belocated adjacent to one another (e.g., different locations of agenerally planar surface). In this example, two temperature sensors maybe mounted to the same side of a hybrid board and oriented toward theirrespective surfaces. In other examples, the two surfaces may begenerally opposed to one another (e.g., surfaces separated by a hybridboard carrying each of the temperature sensors). In this example, eachtemperature sensor may be mounted on opposing sides of the hybrid boardsuch that one sensor senses temperature on one side of the hybrid boardand the other sensor senses temperature on the opposite side off thehybrid board.

Each temperature sensor may sense temperatures simultaneously such thatsystem 10 may process multiple temperatures at the same time.Alternatively, one or more temperature sensors may be selectivelyenabled by one or more processors. This selective temperature sensingmay reduce power consumption from unnecessary temperature sensors. Inaddition, selective temperature sensing may reduce power consumptionand/or processing speed needed to process signals from unneededtemperature sensors. In one example, each of the plurality of IRtemperature sensors may include a shutter that opens to detect IR energyand closes to prevent IR energy detection. The processor may select tosense the temperature of a first portion of the device with a firsttemperature sensor instead of a second portion of the device with asecond temperature sensor. Responsive to the selection, the processormay control a first shutter of the first temperature sensor to open andcontrol a second shutter of the second temperature sensor to close.Alternatively or additionally, the processor may selectively send powerto desired temperature sensors to sense the temperature of a portion ofthe device associated with the selected portion.

In some examples, a phase change material may be used to facilitatetemperature sensing of one or more components of the device. The phasechange material may be disposed on the surface of a component from whichtemperature is to be sensed. The component may be a housing of thedevice, a coil that transfers energy to rechargeable power source 18during charging (e.g., a primary or secondary coil), or any othercomponent within the device. The phase change material may providemultiple advantages to sensing the desired temperature. The phase changematerial may function as a heat sink to reduce the temperature of thecomponent to which the phase change material is in contact. In addition,the phase change material may distribute temperatures across thecomponent and reduce the frequency and/or intensities of temperaturevariation (e.g., hot spots). In some examples, the phase change materialmay even facilitate temperature detection from a material with adifficult to detect emissivity. In some examples, the phase changematerial may be disposed on only a portion of a component. In otherexamples, the phase change material may be disposed over the entiresurface of the component. The phase change material may be encapsulatedby a membrane, embedded in a woven fabric, or otherwise disposed in atleast partial contact with a surface of the component.

System 10 may control the charging of rechargeable power source 18 usingone or more techniques. Using the sensed temperature, a processor maycompare the sensed temperature to a threshold temperature. The sensedtemperature may be from a temperature sensor located within IMD 14and/or charging device 22. The threshold temperature may be a valuestored by a memory. The threshold temperature may be selected based ontissue models, patient history, or any other information that may beused to determine when a charging session should be modified. Theprocessor may then determine when the sensed temperature exceeds thethreshold temperature. When the sensed temperature exceeds the thresholdtemperature, the processor may control charging of rechargeable powersource 18 by adjusting a power level used to charge rechargeable powersource 18. In other words, the processor may reduce the power level whenthe temperature threshold is exceeded, turn the power off for apredetermined period of time before the power is again provided (e.g.,cycle the power on and off) or even terminate the charging session.Reducing the power level may reduce the energy used to chargerechargeable power source 18 and/or the rate at which rechargeable powersource 18 is recharged.

When sensing a temperature of a component of IMD 14, a processor of IMDmay merely transmit the calculated temperature or data representative ofthe temperature to charging device 22. A processor of charging device 22may then determine how to control the charging session. Alternatively,the processor of IMD 14 may determine how to control the chargingsession and transmit a respective command to charging device 22.

Charging device 22 may thus charge rechargeable power source 18 usingone or more power levels or cycle times in some examples. In oneexample, charging device 22 may select a high power level when firststarting a charging session. Charging device 22 may then select a lowpower level, relative to the high power level, in response to one ormore temperature sensors exceeding a threshold. In this manner, the highpower level may charge rechargeable power source 18 at a high rate toreduce charging time while increasing the temperature of IMD 14.Charging device 22 may select the low power level to charge rechargeablepower source 18 at a slower rate to reduce the temperature of IMD 14.The low power level may be sufficiently minimal so that any increase intemperature of IMD 14 may have minimal or no effect on surroundingtissue.

A high power level and a low power level may be subjective and relativeto the charging power that charging device 22 is capable of generatingand transmitting to IMD 14. In some cases, the high power level may bethe maximum power that charging device 22 can generate. This high powerlevel may be referred to as a “boost” or “accelerated” charging levelbecause of the high rate of charge induced in rechargeable power source18. This high rate of charge may minimize the amount of time patient 12needs to recharge rechargeable power source 18. By monitoring thetemperature of one or more portions of charging head 26 and/or IMD 14,charging device 22 may charge rechargeable power source 18 with the highpower level for a longer period of time without damaging tissuesurrounding IMD 14.

In one example, the high power level may be approximately 2.5 Watts andthe low power level may be approximately 1.0 Watt (W). Of course otherpower levels and ranges may be selected for use, with such levelsfalling either within the above-described range or outside of thisrange. For instance, a low power level may be much lower than 1.0 Wattin an example wherein there is good coupling between primary and secondcoils and wherein recharge is to be conducted relatively slowly. Anexample charge current level may be approximately 100 milliamps (mA) forthe high power level and approximately 60 mA for the low power level. Anexample primary coil voltage and current for a high power may beapproximately 450 V and approximately 800 mA, respectively, and anexample primary coil voltage and current for a low power level may beapproximately 250 V and approximately 500 mA. These values are merelyexamples, and other examples may include higher or lower values inaccordance with the techniques described herein. In additional more thantwo levels may be defined (e.g., low, one or more intermediate levels,and a high level) to control charging.

In some cases, charging device 22 may cycle the driving of the primarycoil. For instance, charging device 22 may drive the coil during a firstperiod of time, and may discontinue driving the coil for a second periodof time following the first period of time. This may be repeatedmultiple times, with the first and second time periods being selected tocontrol an overall transmission of power (and hence heat dissipation.)

In some examples, IMD 14 may directly adjust the power level forcharging (e.g., limit the charge current) instead of relying on a changein power level at charging device 22. For example, as IMD 14 receives analternating charging current, IMD 14 may employ a circuit that maychange from full-wave rectification to half-wave rectification to reducethe charge rate and temperature of IMD 14 during charging. In otherwords, IMD 14 may utilize half-wave rectification as a means to reducethe electrical current delivered to rechargeable power supply 18 insteadof reducing the overall power received by IMD 14. Alternatively, IMD 14may employ other mechanisms such as current and/or voltage limiters thatmay limit the charging rate of rechargeable power supply 18.

In other examples, a processor of charging device 22 and/or IMD 14 mayperform actions other than changing a power level for charging inresponse to temperature changes. For example, charging device 22 mayinstruct a user to replace a phase change material cartridge attached tocharging head 26 of charging device 22. The phase change materialcartridge may act as a heat sink and increase the amount of timecharging device 22 can charge rechargeable power source 18 at a highpower level. In one example, a processor of charging device 22 maycalculate a temperature change rate from the multiple sensedtemperatures when rechargeable power source 18 is charging. Thetemperature change rate may be representative of how fast thetemperature of charging head 26 is changing. As described above,charging head 26 may include a primary coil that transfers powerwirelessly to a secondary coil within IMD 14. The processor may thendetermine when the temperature change rate increases subsequent to thetemperature change rate decreasing during the charging. In response todetermining that the temperature change rate has increased, theprocessor may control a user interface to present a notification thatinstructs a user to replace a phase change material cartridge thermallycoupled to the device.

In other words, the processor may identify inflection points as thetemperature changes. Once the temperature of the phase change materialreaches the melting point of the material, additional heat istransferred into changing the phase of the material instead of raisingthe temperature. However, after the material has changed phase, thesensed temperature may again increase. Upon this detected increase intemperature, charging device 22 may determine that the phase changematerial is no longer capable of suppressing the temperature increasesof charging head 26. Since the cartridge may be replaceable, chargingdevice 22 may present a visual, audio, or tactile notification thatinstructs the user to replace the cartridge. If the user does notreplace the cartridge prior to the temperate exceeding a threshold,charging device 22 may then reduce the power level of charging orterminate the charging session.

As described herein, a non-thermally coupled temperature sensor may beused to sense a temperature of a portion of IMD 14 (includingrechargeable power source 18), charging head 26, and/or housing 24. Aprocessor that controls an aspect of the charging session may be housedby IMD 14, charging head 26, or housing 24. In this manner, a processorconfigured to perform some or all of the functions described herein maybe housed together with a temperature sensor or separate from thetemperature sensor.

Although an implantable rechargeable power source 18 is generallydescribed herein, techniques of this disclosure may also be applicableto a rechargeable power source 18 that is not implanted. For example,rechargeable power source 18 may be external to the skin of patient 12and in physical contact with the skin. Therefore, charging device 22 maycontrol the charging of rechargeable power source 18 with temperaturesensed within charging head 26 or IMD 14 even when the power source isexternal to patient 12.

FIG. 2 is a block diagram illustrating example components of IMD 14. Inthe example of FIG. 2, IMD 14 includes temperature sensor 39, coil 40,processor 30, therapy module 34, recharge module 38, memory 32,telemetry module 36, and rechargeable power source 18. In otherexamples, IMD 14 may include a greater or a fewer number of components.For example, in some examples, IMD 14 may not include temperature sensor39.

In general, IMD 14 may comprise any suitable arrangement of hardware,alone or in combination with software and/or firmware, to perform thevarious techniques described herein attributed to IMD 14 and processor30. In various examples, IMD 14 may include one or more processors 30,such as one or more microprocessors, digital signal processors (DSPs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or any other equivalent integrated or discretelogic circuitry, as well as any combinations of such components. IMD 14also, in various examples, may include a memory 32, such as randomaccess memory (RAM), read only memory (ROM), programmable read onlymemory (PROM), erasable programmable read only memory (EPROM),electronically erasable programmable read only memory (EEPROM), flashmemory, comprising executable instructions for causing the one or moreprocessors to perform the actions attributed to them. Moreover, althoughprocessor 30, therapy module 34, recharge module 38, and telemetrymodule 36 are described as separate modules, in some examples, processor30, therapy module 34, recharge module 38, and telemetry module 36 arefunctionally integrated. In some examples, processor 30, therapy module34, recharge module 38, and telemetry module 36 correspond to individualhardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

Memory 32 may store therapy programs or other instructions that specifytherapy parameter values for the therapy provided by therapy module 34and IMD 14. In some examples, memory 32 may also store temperature datafrom temperature sensor 39, instructions for recharging rechargeablepower source 18, thresholds, instructions for communication between IMD14 and charging device 22, or any other instructions required to performtasks attributed to IMD 14. Memory 32 may be configured to storeinstructions for communication with and/or controlling one or moretemperature sensors 39. As described herein, the non-thermally coupledtemperature sensor 39 may be an IR sensor, a phosphor temperaturesensor, or any other non-contact sensor or sensor (whether or notcontact) that senses temperature by means other than thermal coupling.

Generally, therapy module 34 may generate and deliver electricalstimulation under the control of processor 30. In some examples,processor 30 controls therapy module 34 by accessing memory 32 toselectively access and load at least one of the stimulation programs totherapy module 34. For example, in operation, processor 30 may accessmemory 32 to load one of the stimulation programs to therapy module 34.In such examples, relevant stimulation parameters may include a voltageamplitude, a current amplitude, a pulse rate, a pulse width, a dutycycle, or the combination of electrodes 17A, 17B, 17C, and 17D thattherapy module 34 uses to deliver the electrical stimulation signal.Therapy module 34 may be configured to generate and deliver electricalstimulation therapy via one or more of electrodes 17A, 17B, 17C, and 17Dof lead 16. Alternatively, or additionally, therapy module 34 may beconfigured to provide different therapy to patient 12. For example,therapy module 34 may be configured to deliver drug delivery therapy viaa catheter. These and other therapies may be provided by IMD 14.

IMD also includes components to receive power from charging device 22 torecharge rechargeable power source 18 when rechargeable power source 18has been at least partially depleted. As shown in FIG. 2, IMD 14includes secondary coil 40 and recharge module 38 coupled torechargeable power source 18. Recharge module 38 may be configured tocharge rechargeable power source 18 with the selected power leveldetermined by either processor 30 or charging device 22. Recharge module38 may include any of a variety of charging and/or control circuitryconfigured to process or convert current induced in coil 40 intocharging current to charge power source 18. Although processor 30 mayprovide some commands to recharge module 38, in some examples, processor30 may not need to control any aspect of recharging.

Secondary coil 40 may include a coil of wire or other device capable ofinductive coupling with a primary coil disposed external to patient 12.Although secondary coil 40 is illustrated as a simple loop of in FIG. 2,secondary coil 40 may include multiple turns of conductive wire.Secondary coil 40 may include a winding of wire configured such that anelectrical current can be induced within secondary coil 40 from amagnetic field. The induced electrical current may then be used torecharge rechargeable power source 18. In this manner, the electricalcurrent may be induced in secondary coil 40 associated with rechargeablepower source 18. The induction may be caused by electrical currentgenerated in the primary coil of charging device 22, where the level ofthe current may be based on the selected power level. The couplingbetween secondary coil 40 and the primary coil of charging device 22 maybe dependent upon the alignment of the two coils. Generally, thecoupling efficiency increases when the two coils share a common axis andare in close proximity to each other. Charging device 22 and/or IMD 14may provide one or more audible tones or visual indications of thealignment.

Although inductive coupling is generally described as the method forrecharging rechargeable power source 18, other wireless energy transfertechniques may alternatively be used. Any of these techniques maygenerate heat in IMD 14 such that the charging process can be controlledby matching the sensed temperature to one or more thresholds, modelingtissue temperatures based on the sensed temperature, or using acalculated cumulative thermal dose as feedback.

Recharge module 38 may include one or more circuits that process,filter, convert and/or transform the electrical signal induced insecondary coil to an electrical signal capable of rechargingrechargeable power source 18. For example, in alternating currentinduction, recharge module 38 may include a half-wave rectifier circuitand/or a full-wave rectifier circuit configured to convert alternatingcurrent from the induction to a direct current for rechargeable powersource 18. The full-wave rectifier circuit may be more efficient atconverting the induced energy for rechargeable power source 18. However,a half-wave rectifier circuit may be used to store energy inrechargeable power source 18 at a slower rate. In some examples,recharge module 38 may include both a full-wave rectifier circuit and ahalf-wave rectifier circuit such that recharge module 38 may switchbetween each circuit to control the charging rate of rechargeable powersource 18 and temperature of IMD 14.

Rechargeable power source 18 may include one or more capacitors,batteries, and/or other energy storage devices. Rechargeable powersource 18 may deliver operating power to the components of IMD 14. Insome examples, rechargeable power source 18 may include a powergeneration circuit to produce the operating power. Rechargeable powersource 18 may be configured to operate through hundreds or thousands ofdischarge and recharge cycles. Rechargeable power source 18 may also beconfigured to provide operational power to IMD 14 during the rechargeprocess. In some examples, rechargeable power source 18 may beconstructed with materials to reduce the amount of heat generated duringcharging. In other examples, IMD 14 may be constructed of materials thatmay help dissipate generated heat at rechargeable power source 18,recharge module 38, and/or secondary coil 40 over a larger surface areaof the housing of IMD 14.

Although rechargeable power source 18, recharge module 38, and secondarycoil 40 are shown as contained within the housing of IMD 14, inalternative implementations, at least one of these components may bedisposed outside of the housing. For example, in some implementations,secondary coil 40 may be disposed outside of the housing of IMD 14 tofacilitate better coupling between secondary coil 40 and the primarycoil of charging device 22. These different configurations of IMD 14components may allow IMD 14 to be implanted in different anatomicalspaces or facilitate better inductive coupling alignment between theprimary and secondary coils.

IMD 14 may also include temperature sensor 39. Temperature sensor 39 mayinclude one or more non-thermally coupled temperature sensors configuredto measure the temperature of respective portions of IMD 14. Asdescribed herein, a non-thermally coupled temperature sensor is notthermally coupled to, and may not be directly attached to, the portionof the device from which temperature is to be measured. In one instance,the temperature sensor is not directly attached to the portion of thedevice. In other words, temperature measurement is not performed throughdirect contact or physical contact between the temperature sensor andthe target portion to be measured. Although the temperature sensor maybe physically attached to the target portion or target surface throughone or more structures, any thermal conduction that may occur betweenthe target portion and the sensor is not used to measure the temperatureof the target portion.

Temperature sensor 39 may be oriented to measure the temperature of acomponent, surface or structure (e.g., secondary coil 40, power source19, recharge module 38, or the housing) of IMD 14. Temperature sensor 39may be disposed internal of the housing of IMD 14 or otherwise disposedrelative to the external portion of housing (e.g., tethered to anexternal surface of housing via an appendage cord). As described herein,temperature sensor 39 may be used to use non-contact temperaturemeasurements of IMD 14 to infer the temperature of tissue surroundingand/or contacting the housing of IMD 14. Processor 30, or chargingdevice 22, may use this temperature measurement as the tissuetemperature feedback to control the power levels or charge times (e.g.,cycle times) used during the charging session. Although a singletemperature sensor may be adequate, multiple temperature sensors mayprovide more specific temperature readings of separate components ordifferent areas of the housing. Although processor 30 may continuallymeasure temperature using temperature sensor 39, processor 30 mayconserve energy by only measuring temperature during recharge sessions.Further, temperature may be sampled at a rate necessary to effectivelycontrol the charging session, but the sampling rate may be reduced toconserve power as appropriate.

Processor 30 may also control the exchange of information with chargingdevice 22 and/or an external programmer using telemetry module 36.Telemetry module 36 may be configured for wireless communication usingradio frequency protocols or inductive communication protocols.Telemetry module 36 may include one or more antennas configured tocommunicate with charging device 22, for example. Processor 30 maytransmit operational information and receive therapy programs or therapyparameter adjustments via telemetry module 36. Also, in some examples,IMD 14 may communicate with other implanted devices, such asstimulators, control devices, or sensors, via telemetry module 36. Inaddition, telemetry module 36 may be configured to transmit the measuredtissue temperatures from temperature sensor 39, for example.

In other examples, processor 30 may transmit additional information tocharging device 22 related to the operation of rechargeable power source18. For example, processor 30 may use telemetry module 36 to transmitindications that rechargeable power source 18 is completely charged,rechargeable power source 18 is fully discharged, or any other chargestatus of rechargeable power source 18. Processor 30 may also transmitinformation to charging device 22 that indicates any problems or errorswith rechargeable power source 18 that may prevent rechargeable powersource 18 from providing operational power to the components of IMD 14.

FIG. 3 is a block diagram of the example external charging device 22.While charging device 22 may generally be described as a hand-helddevice, charging device 22 may be a larger portable device or a morestationary device. In addition, in other examples, charging device 22may be included as part of an external programmer or includefunctionality of an external programmer. In addition, charging device 22may be configured to communicate with an external programmer. As shownin FIG. 3, charging device 22 includes two separate components. Housing24 encloses components such as a processor 50, memory 52, user interface54, telemetry module 56, and power source 60. Charging head 26 mayinclude power module 58, temperature sensor 59, and coil 48. A differentpartitioning of components is also possible, such as including one ormore of the foregoing components within a module carried by the cord ofcharging device 22.

A separate charging head 26 may facilitate optimal positioning of coil48 over coil 40 of IMD 14. However, charging module 58 and/or coil 48may be integrated within housing 24 in other examples. Memory 52 maystore instructions that, when executed by processor 50, cause processor50 and external charging device 22 to provide the functionality ascribedto external charging device 22 throughout this disclosure.

External charging device 22 may also include one or more non-thermallycoupled temperature sensors 59, similar to temperature sensor 39 of FIG.2. Temperature sensor 59 may be disposed within charging head 26 and/orhousing 24. For example, charging head 26 may include one or morenon-thermally coupled temperature sensors positioned and configured tosense the temperature of coil 48 and/or a surface of the housing ofcharging head 26. In some examples, charging device 22 may not includetemperature sensor 59.

In general, charging device 22 comprises any suitable arrangement ofhardware, alone or in combination with software and/or firmware, toperform the techniques attributed to charging device 22, and processor50, user interface 54, telemetry module 56, and charging module 58 ofcharging device 22. In various examples, charging device 22 may includeone or more processors, such as one or more microprocessors, DSPs,ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Chargingdevice 22 also, in various examples, may include a memory 52, such asRAM, ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, a CD-ROM,comprising executable instructions for causing the one or moreprocessors to perform the actions attributed to them. Moreover, althoughprocessor 50 and telemetry module 56 are described as separate modules,in some examples, processor 50 and telemetry module 56 are functionallyintegrated. In some examples, processor 50 and telemetry module 56 andcharging module 58 correspond to individual hardware units, such asASICs, DSPs, FPGAs, or other hardware units.

Memory 52 may store instructions that, when executed by processor 50,cause processor 50 and charging device 22 to provide the functionalityascribed to charging device 22 throughout this disclosure. For examplememory 52 may include instructions that cause processor 50 to controlthe power level used to charge IMD 14 in response to the sensedtemperatures, communicate with IMD 14, or instructions for any otherfunctionality. In addition, memory 52 may include a record of selectedpower levels, sensed temperatures, or any other data related to chargingrechargeable power source 18. Processor 50 may, when requested, transmitany of this stored data in memory 52 to another computing device forreview or further processing.

User interface 54 may include a button or keypad, lights, a speaker forvoice commands, a display, such as a liquid crystal (LCD),light-emitting diode (LED), or cathode ray tube (CRT). In some examplesthe display may be a touch screen. As discussed in this disclosure,processor 50 may present and receive information relating to thecharging of rechargeable power source 18 via user interface 54. Forexample, user interface 54 may indicate when charging is occurring,quality of the alignment between coils 40 and 48, the selected powerlevel, current charge level of rechargeable power source 18, duration ofthe current recharge session, anticipated remaining time of the chargingsession, sensed temperatures, instructions for changing a phase changematerial cartridge of charging head 26, or any other information.Processor 50 may receive some of the information displayed on userinterface 54 from IMD 14 in some examples.

User interface 54 may also receive user input via user interface 54. Theinput may be, for example, in the form of pressing a button on a keypador selecting an icon from a touch screen. The input may request startingor stopping a recharge session, a desired level of charging, or one ormore statistics related to charging rechargeable power source 18 (e.g.,the cumulative thermal dose). In this manner, user interface 54 mayallow the user to view information related to the charging ofrechargeable power source 18 and/or receive charging commands.

Charging device 22 also includes components to transmit power torecharge rechargeable power source 18 associated with IMD 14. As shownin FIG. 3, charging device 22 includes primary coil 48 and chargingmodule 58 coupled to power source 60. Charging module 58 may beconfigured to generate an electrical current in primary coil 48 fromvoltage stored in power source 60. Although primary coil 48 isillustrated as a simple loop in FIG. 3, primary coil 48 may includemultiple turns of wire. Charging module 58 may generate the electricalcurrent according to a power level selected by processor 50 based on thesensed temperature or temperatures received from IMD 14 or a temperaturesensor within charging device 22. As described herein, processor 50 mayselect a high power level, low power level, or a variety of differentpower levels to control the rate of recharge in rechargeable powersource 18 and the temperature of IMD 14. In some examples, processor 50may control charging module 58 based on a power level selected byprocessor 30 of IMD 14. The sensed temperature used as feedback forcontrol of the recharge power level may be from a temperature sensed bya temperature sensor within IMD 14 and/or charging device 22. Althoughprocessor 50 may control the power level used for charging rechargeablepower source 18, charging module 58 may include one or more processorsconfigured to partially or fully control the power level based on thesensed temperatures.

Primary coil 48 may include a coil of wire, e.g., having multiple turns,or other device capable of inductive coupling with a secondary coil 40disposed within patient 12. Primary coil 48 may include a winding ofwire configured such that an electrical current generated within primarycoil 48 can produce a magnetic field configured to induce an electricalcurrent within secondary coil 40. The induced electrical current maythen be used to recharge rechargeable power source 18. In this manner,the electrical current may be induced in secondary coil 40 associatedwith rechargeable power source 18. The coupling efficiency betweensecondary coil 40 and primary coil 48 of charging device 22 may bedependent upon the alignment of the two coils. Generally, the couplingefficiency increases when the two coils share a common axis and are inclose proximity to each other. User interface 54 of charging device 22may provide one or more audible tones or visual indications of thealignment.

Charging module 58 may include one or more circuits that generate anelectrical signal, and an electrical current, within primary coil 48.Charging module 58 may generate an alternating current of specifiedamplitude and frequency in some examples. In other examples, chargingmodule 58 may generate a direct current. In any case, charging module 58may be capable of generating electrical signals, and subsequent magneticfields, to transmit various levels of power to IMD 14. In this mannercharging module 58 may be configured to charge rechargeable power source18 of IMD 14 with the selected power level.

The power level that charging module 58 selects for charging may be usedto vary one or more parameters of the electrical signal generated forcoil 48. For example, the selected power level may specify wattage,electrical current of primary coil 48 or secondary coil 40, currentamplitude, voltage amplitude, pulse rate, pulse width, a cycling ratethat determines when the primary coil is driven, or any other parameterthat may be used to modulate the power transmitted from coil 48. In thismanner, each power level may include a specific parameter set thatspecifies the signal for each power level. Changing from one power levelto another power level (e.g., a high power level to a lower power level)may include adjusting one or more parameters. For instance, at a highpower level, the primary coil may be substantially continuously driven,whereas at a lower power level, the primary coil may be intermittentlydriven such that periodically the coil is not driven for a predeterminedtime to control heat dissipation. The parameters of each power level maybe selected based on hardware characteristics of charging device 22and/or IMD 14.

Power source 60 may deliver operating power to the components ofcharging device 22. Power source 60 may also deliver the operating powerto drive primary coil 48 during the charging process. Power source 60may include a battery and a power generation circuit to produce theoperating power. In some examples, a battery of power source 60 may berechargeable to allow extended portable operation. In other examples,power source 60 may draw power from a wired voltage source such as aconsumer or commercial power outlet.

Charging device 22 may include one or more non-thermally coupledtemperature sensor 59 (e.g., similar to temperature sensor 39 of IMD 14)for sensing the temperature of a portion of the device. For example,temperature sensor 59 may be disposed within charging head 26 andoriented to sense the temperature of the housing of charging head 26. Inanother example, temperature sensor 59 may be disposed within charginghead 26 and oriented to sense the temperature of charging module 58and/or coil 48. In other examples, charging device 22 may includemultiple temperature sensors 59 each oriented to any of these portionsof device to manage the temperature of the device during chargingsessions.

Telemetry module 56 supports wireless communication between IMD 14 andcharging device 22 under the control of processor 50. Telemetry module56 may also be configured to communicate with another computing devicevia wireless communication techniques, or direct communication through awired connection. In some examples, telemetry module 56 may besubstantially similar to telemetry module 36 of IMD 14 described herein,providing wireless communication via an RF or proximal inductive medium.In some examples, telemetry module 56 may include an antenna, which maytake on a variety of forms, such as an internal or external antenna.Although telemetry modules 56 and 36 may each include dedicatedantennae, telemetry modules 56 and 36 may instead, or additionally, beconfigured to utilize inductive coupling from coils 40 and 48 totransfer data.

Examples of local wireless communication techniques that may be employedto facilitate communication between charging device 22 and IMD 14include radio frequency and/or inductive communication according to anyof a variety of standard or proprietary telemetry protocols, oraccording to other telemetry protocols such as the IEEE 802.11x orBluetooth specification sets. In this manner, other external devices maybe capable of communicating with charging device 22 without needing toestablish a secure wireless connection. As described herein, telemetrymodule 56 may be configured to receive a signal or data representativeof a measured tissue temperature from IMD 14. The tissue temperature maybe indirectly measured by measuring the temperature of the internalsurface of the IMD housing adjacent to rechargeable power source 18. Insome examples, multiple temperature readings by IMD 14 may be averagedor otherwise used to produce a single temperature value that istransmitted to charging device 22. The sensed temperature may be sampledand/or transmitted by IMD 14 (and received by charging device 22) atdifferent rates, e.g., on the order of microseconds, milliseconds,seconds, minutes, or even hours. Processor 50 may then use the receivedtemperature to control charging of rechargeable power source 18 (e.g.,control the charging level used to recharge power source 18).

FIGS. 4A-4C are conceptual cross-sectional diagrams illustrating exampletemperature sensors disposed 80, 96, and 112 within respective IMDs 70,86, and 102. IMDs 70, 86, and 102 are examples of IMD 14, and each oftemperature sensors 80, 96, and 112 are examples of non-thermallycoupled temperature sensor 39. Although temperature sensors may bedescribed with respect to a specific type of device such as an IMD, thetemperature sensors may alternatively be disposed within a differenttype of device such as charging device 22 (e.g., within housing 24 orcharging head 26). IR temperature sensors are provided as an examplesensor in FIGS. 4A-4C. The IMDs described herein are generally shownwith rectangular cross-sections. However, non-thermally coupledtemperature sensors may be disposed within IMDs or any other devices ofany shapes, dimensions, or sizes.

As shown in FIG. 4A, IMD 70 includes housing 72 that encloses hybridboard 74, electronics 76 and 78, and temperature sensor 80. Hybrid board74 may be mounted or secured within housing 72. Electronics 76 and 78may include various components such as a processor and memory andassociated circuitry. Although not shown in FIG. 4A, a secondary coiland rechargeable power source may also be disposed within housing 72.Temperature sensor 80 may be mounted onto a surface of hybrid board 74.

Temperature sensor 80 may be an infrared temperature sensor oriented ina specific manner to detect infrared radiation emitted from a desiredlocation of housing 72. Portion 82 may be an area of housing 72 fromwhich the temperature is to be sensed. Portion 82 may emit IR energy 84as a function of the temperature of portion 82. As IR energy 84 isemitted from portion 82, temperature sensor 80 may detect at least someof IR energy 84 and output a signal representative of the intensity ofIR energy 84. Although IR energy 84 may be emitted in several directionsfrom portion 82, temperature sensor 80 may only detect the IR energydirectly transmitted from portion 82.

IR energy 84 may travel through a vacuum, a gas, or other mediumseparating temperature sensor 80 from portion 82. In some examples,temperature sensor 80 may be disposed in close proximity to portion 82.However, temperature sensor 80 may sense the temperature of portion 82via IR energy 84 instead of heat conducted between portion 82 andtemperature sensor 80. Instead of being oriented toward portion 82,temperature sensor 80 may detect IR energy from other portions ofhousing 72 or even other components (e.g., a component of electrodes 78.

As shown in FIG. 4B, IMD 86 includes housing 88 that encloses hybridboard 90, electronics 92 and 94, and temperature sensors 96A, 96B, and96C (collectively “temperature sensors 96”). Hybrid board 90 may bemounted or secured within housing 88. Temperature sensors 96 may be IRtemperature sensors oriented in a specific manner to detect infraredradiation emitted from specific locations of housing 88. Portions 98A,98B, and 98C (collectively “portions 98”) are respective areas ofhousing 88 from which the temperature is to be sensed. Differentportions 98 may be sensed for temperature differences due to variationsin temperature caused by components within housing 88 or externalinfluences. Each of portions 98 may emit IR energy 100 as a function ofthe temperature of the respective portions 98. However, each oftemperature sensors 96 are oriented to receive the portion of IR energy100 emitted from the respective portion 98. Therefore, temperaturesensors 96 may sense variations in temperature between the differentportions 98.

The variations in temperature between portions 98 may be used togenerate an average temperature of housing 88, a weighted average, oridentify one or more hot spots of housing 88. In other examples, themultiple temperature measurements of portions 98 may be used to generatea temperature gradient that models the temperature at differentlocations of housing 88. Charging device 22 may then control powerlevels for charging based on temperature of one or more hot spots, basedon the detected gradient, or based on another aspect of the temperaturereadings to prevent sensitive tissues, for example, from being exposedto undesirable temperatures.

Temperature sensors 96 are all disposed on the same side of hybrid board90. Although temperature sensors 96A and 96C are oriented atnon-orthogonal angles with respect to housing 88, other sensors may bepositioned at orthogonal angles in other examples. In addition, multipletemperature sensors may be disposed at any location, and with anyorientation, within housing 88. For example, each temperature sensor 96may be mounted at a location on hybrid board 90 that would be closest tothe desired portion of housing 88 for temperature sensing. In thismanner, temperature sensors may be selected to be positioned at anylocation within housing 88.

As shown in FIG. 4C, in another example, IMD 102 includes housing 104that encloses hybrid board 106, electronics 108 and 110, and temperaturesensors 112A and 112B (collectively “temperature sensors 112”). Hybridboard 106 may be mounted or secured within housing 104. Temperaturesensors 112 may be IR temperature sensors oriented in a specific mannerto detect infrared radiation emitted from specific locations of housing104. In the example of IMD 102, temperature sensors 112 may bepositioned to sense the temperature of opposing surfaces of housing 104.In other words, portions 114A and 114B (collectively “portions 114”) aregenerally opposite each other. In some examples, sensing the temperatureon opposing sides of IMD 102 may be beneficial if IMD 102 becomesflipped within the tissue pocket containing IMD 102 within patient 12.In other words, IMD 102 may be configured to determine that a flip hasoccurred and/or measure the temperature of a desired surface of housing104 regardless of if IMD 102 has flipped within patient 12.

Since hybrid board 106 separates portions 114A and 114B, temperaturesensors 112A and 112B may be mounted on opposing surfaces of hybridboard 106. Each of temperature sensors 112 may thus be oriented toreceive IR energy 116A and 116B from respective portions 114A and 114B.In other examples, temperature sensors 112 may be mounted on the sameside of hybrid board 106 and still capable of detecting IR energy 116Aand 116B. For example, a hole or window may be formed in hybrid board106 such that the IR energy can pass through hybrid board and to theappropriate temperature sensor. By positioning multiple non-thermallycoupled temperature sensors within IMD 102, the temperature at differentlocations of housing 104 or at different locations internal to IMD maybe sensed and used to control the charging of rechargeable power source18. For example, external charging device 22 may control the power levelused to recharge power source 18 based on the measured temperatureswithin IMD 102.

FIGS. 5A and 5B are conceptual cross-sectional diagrams illustratingexample temperature sensor 132 and 150 and respective structures thattransfer energy associated with a desired portion of an IMD. IMDs 120and 140 are examples of IMD 14, and each of temperature sensors 132 and150 are examples of non-thermally coupled temperature sensor 39. IRtemperature sensors are provided as an example sensor in FIGS. 5A and5B, and may be similar to temperature sensor 80 of FIG. 4A.

As shown in FIG. 5A, IMD 120 includes housing 122 that encloses hybridboard 124, electronics 126 and 128, and temperature sensor 132. Hybridboard 124 may be mounted or secured within housing 122. Electronics 126and 128 may include various components such as a processor and memory.Although not shown in FIG. 5A, a secondary coil and rechargeable powersource may also be disposed within housing 122. Temperature sensor 132may be mounted onto a surface of hybrid board 124.

In addition to temperature sensor 132, heat pipe 130 may be disposedwithin housing 122 to transfer energy from portion 134 to temperaturesensor 132. In some examples, the desired area from which temperature isto be sensed may not be within line-of-sight from temperature sensor132. However, heat pipe 130 (or another energy transfer structure) maytransfer the energy from the desired surface or object to temperaturesensor 132. In the example of FIG. 5A, heat pipe 132 may be configuredto be thermally coupled to portion 134 of housing 122. Heat pipe 132 maybe a thermally conductive such that the temperature of portion 134 isapproximately similar to any location along heat pipe 130. Since portion136 of heat pipe 136 may also emit IR energy 138, temperature sensor 132may detect IR energy 138 as a representation of the temperature ofportion 134 of housing 122. In some cases, a function (e.g., amathematical function) may be employed to convert the heat detected byheat pipe 136 into a representation of the heat of portion 134 ofhousing. For instance, this may involve multiplying the detected heat bya constant that takes into account effects caused by heat pipe.

Although only one heat pipe 130 is provided, IMD 120 may include two ormore heat pipes to transfer energy from multiple portions within IMD120. Heat pipe 132 may be constructed of a solid structure, hollowstructure, or any other configuration in which the material of heat pipe132 conducts heat energy from the target surface (e.g., portion 134) totemperature sensor 150.

Temperature sensor 132 may be an infrared temperature sensor oriented ina specific manner to detect IR energy 138 from heat pipe 130. Portion136 may emit IR energy 138 as a function of the temperature of portion136 and portion 134. As IR energy 138 is emitted from portion 136,temperature sensor 132 may detect at least some of IR energy 138 andoutput a signal representative of the intensity of IR energy 138.Although IR energy 138 may be emitted in several directions from portion136, temperature sensor 132 may only detect the IR energy directlytransmitted from portion 136.

In some examples, the emissivity of portion 136 of heat pipe 130 maydiffer from the emissivity of portion 134 of housing 122. Thisemissivity difference may arise from the materials used for heat pipe130 and housing 122 being dissimilar. For example, housing 122 may beconstructed of a titanium alloy and heat pipe 130 may be constructed ofcopper or a copper alloy. The material may be solid, hollow, or anyother continuous material configuration. In other words, heat pipe 130may be constructed of a material with higher thermal conductivity thanthe material used in housing 122. Therefore, a processor may calibratetemperature sensor 132 to account for differences in emissivity betweenheat pipe 130 and housing 122. Such calibration may be performed insteadof, or in addition to, use of a mathematical function for deriving theheat of portion 134 from the heat sensed from portion 136.

Heat pipe 130 may be configured within housing 122 to physically contactportion 134 of housing 122. In one example, heat pipe 130 may be mounteddirectly to housing 122 via conductive adhesive, spot welding, or anyother technique. In another example, heat pipe 130 may be mounted tohybrid board 124 or another location internal to housing 122. In thisexample, heat pipe 130 may be constructed such that a free end of heatpipe 130 is biased against portion 134 of housing 122 when housing 122is hermetically sealed around the interior components of IMD 120. Inother words, closing housing 122 may cause portion 134 to contact heatpipe 130 such that the structural stiffness of heat pipe 130 retainsphysical contact between heat pipe 130 and portion 134.

As shown in FIG. 5B, IMD 140 may include light pipe 152 instead of heatpipe 130 for transferring energy from a desired portion of IMD 140. IMD40 may be substantially similar to IMD 120 of FIG. 5A. IMD 140 mayinclude housing 142 that encloses hybrid board 144, electronics 146 and148, and temperature sensor 150. Temperature sensor 150 may be mountedonto a surface of hybrid board 144. However, light pipe 152 may transferIR energy 156 from portion 154 of housing 142 to temperature sensor 150.

Light pipe 152 may be disposed within housing 142 to transfer energyfrom 154 to temperature sensor 150. Light pipe 152 may or may not bethermally coupled to portion 154. However, in either case, heatconducted through materials of light pipe 152 may not be used to sensethe temperature of portion 154. Instead, light pipe 152 may be a conduitfor transferring IR energy 156 from portion 154 to temperature sensor150. Light pipe 152 may include an optical fiber, a series of mirrors,or any other reflective conduit that transmits IR energy 156 emittedfrom portion 154. In other words, IR energy 156 may be transmittedwithin light pipe 156. Although light pipe 152 may be flexible, lightpipe 152 may instead be a substantially rigid structure mounted totemperature sensor 150 and/or hybrid board 144. Light pipe 152 may bephysically separated from portion 154, but an open end of light pipe 154may be sufficiently proximal to portion 154 such that only IR energy 156from the desired portion 154 enters light pipe 152. In other examples,light pipe 154 may physically contact portion 154.

In other examples, a single device may include multiple heat pipesand/or multiple light pipes. In this manner, temperatures from severaldifferent portions of the device may be sensed using any of thestructures or techniques described herein.

FIG. 6 is a conceptual cross-sectional diagram illustrating exampletemperature sensors 96 and respective shutters 162 for selectivelysensing temperature from different portions of IMD 160. IMD 160 is anexample of IMD 86 of FIG. 4B. IMD 160 may include three IR temperaturesensors 96A, 96B, and 96C mounted to hybrid board 90. However, each oftemperature sensors 96 may include a pair of shutters controlled by aprocessor to selectively allow IR energy to enter one or more of sensors96.

Shutters 162A may cover an aperture of temperature sensor 96A, shutters162B may cover an aperture of temperature sensor 96B, and shutters 162Cmay cover an aperture of temperature sensor 96C. Each of shutters 162may block IR energy transfer and be coupled to a motor or actuator thatopens and closes the respective shutter on demand. In other examples,one of more of shutters 162 may be electro-optical such that a controlsignal can be applied to cause a material of the shutter to togglebetween a transparent state and an opaque state. A processor within IMD60 may control the shutters to open when that temperature sensor isselected to sense the temperature of a respective portion of housing 88.For example, shutters 162A may open to receive IR energy from portion98A, shutters 162B may open to receive IR energy from portion 98B, andshutters 162C may open to receive IR energy from portion 98C.

As shown in FIG. 6, shutters 162A and 162B are closed to preventtemperature sensors 96A and 96B, respectively, from sensing temperatureof portions 98A and 98B. However, shutters 162C are open to allow IRenergy 100 to enter the aperture of temperature sensor 96C. Temperaturesensor 96C has thus been selected to sense the temperature of portion98C. Not only may shutters 162C allow IR energy 100 from portion 98C tobe detected by sensor 96C, shutters 162C may block IR energy from otherlocations to be detected by temperature sensor 96C. In other words,shutters 162C may reduce any infrared radiation emitted from non-targetsurfaces. Shutters 162C may thus be positioned to only accept IR energyfrom a desired surface of IMD 160.

Shutters 162 may, as shown in the example of FIG. 6, be rectangular inshape and operate in pairs. In some examples, each temperature sensor 96may include a single shutter. In other examples, each temperature sensor96 may include two or more shutters. For example, the shutters may bepositioned circumferentially around a temperature sensor such that eachshutter slides over another shutter to open or close the aperture of thetemperature sensor. This type of circular shutter may be similar to ashutter for an aperture of a camera.

In some examples, each of temperature sensors 96 may be independentsensors. Alternatively, temperature sensors 96 may be coupled togetherand output a single signal to a processor. The output may thus be theresult of IR energy received from each sensor. In this manner, shutters162 may be selectively opened or closed such that the output signal isonly representative of the desired portion 98A, 98B, and/or 98C.Although shutters 162 are described with respect to temperature sensors96 within IMD 160, shutters may alternatively be used in other medicaldevices, such as charging device 22.

In other examples, one or more of shutters 162 may be constructed of amaterial that can be used to calibrate the output of one or more oftemperature sensors 96. This material may be a “black body” that emitsinfrared radiation at a level independent of the temperature of thematerial. In other words, for at least the temperature ranges expectedwithin IMD 160, the emissivity of the black body (e.g., shutters 162)may be approximately constant. The processor of IMD 160 may thencalibrate the output of sensors 96 to the known temperature representedby the infrared radiation from shutters 162. IMD 160 may perform thiscalibration periodically, every time shutters 162 close, or on commandfrom charging device 22 or another programming device. This calibrationmay also be performed during the manufacturing process for IMD 160.

FIG. 7 is a conceptual cross-sectional diagram illustrating temperaturesensor 180 utilizing phosphor thermometry. IMD 170 may be an example ofIMD 14. As shown in FIG. 7, IMD 170 includes housing 172 that encloseshybrid board 174, electronics 176 and 178, and temperature sensor 180.Hybrid board 174 may be mounted or secured within housing 172.Electronics 176 and 178 may include various components such as aprocessor and memory. Although not shown in FIG. 7, a secondary coil andrechargeable power source may also be disposed within housing 172.Temperature sensor 180 may be mounted onto a surface of hybrid board174.

Temperature sensor 180 may be a phosphor temperature sensor that isoriented in a specific manner to detect the temperature of portion 183of housing 172 using luminescence detected from phosphor material 184.In other words, temperature sensor 180 may be a non-thermally coupledtemperature sensor that utilizes phosphor thermometry. Temperaturesensor 180 may include emitter 182A and detector 182B. Emitter 182 emitselectromagnetic radiation 186 toward phosphor material 184 disposed onthe desired surface or portion 183. Emitted electromagnetic radiation186 then excites phosphor material 184 disposed on portion 183. Acharacteristic of this excitation may be used to determine temperature.In other words, the object from which temperature will be sensed (e.g.,portion 183) may be coated with phosphor material 184 which is excitedsuch that characteristic of the excitation may be used to determine thetemperature.

Detector 182B of temperature sensor 180 may be configured to detectluminescence 188 from phosphor material 184. Based on the temperature ofphosphor material 184, and the thermally coupled portion 183, theluminescence will have a phase shift with respect to the excitationsignal (e.g., radiation 186), when the excitation signal is periodic.The phase shift may have a magnitude that is representative of thetemperature. In some examples, the magnitude will decay faster forhigher temperatures. Temperature sensor 180 detects this phase shift inthe detected luminescence 188 of phosphor material 184 that occurs inresponse to the excitation from electromagnetic radiation 186.Temperature sensor 180 may then determine the temperature of portion 183based on the detected phase shift. In other examples, temperature sensor180 may output a signal representative of the detected phase shift, anda processor (e.g., processor 30 or 50) is configured to determine thetemperature based on the signal output from sensor 180.

Phosphor material 184 may be selected based on the anticipatedtemperatures of housing 172 or the object to which phosphor material 184will be disposed. In some examples, phosphor material 184 may beeuropium doped lanthanum oxysulphide (La₂O₂S:Eu) or europium dopedgadolinium oxysulphide (Gd₂O₂S:Eu). In addition, the emittedelectromagnetic radiation 186 may be selected for the anticipatedtemperatures to be sensed. In general, electromagnetic radiation 186 mayhave a wavelength between approximately 430 nanometers (nm) and 620 nm.In one example, the wavelength of electromagnetic radiation 186 may beapproximately 514 nm. Generally, as the temperature increases, the phaseshift may be decreased.

FIG. 8 is a conceptual cross-sectional diagram illustrating temperaturesensor 198 disposed within external charging device 22. Specifically,temperature sensor 198 may be disposed within charging head 190 of acharging device. Charging head 190 may be an example of charging head26. However, in other examples, temperature sensor 198 may be disposedwithin another housing of charging device 22 or charging head 190 may bedisposed within an external charging device.

As shown in FIG. 8, charging head 190 may include housing 192 thatencloses hybrid board 196, temperature sensor 198, and primary coil 194.Primary coil 194 may be an example of primary coil 48 of FIG. 3.Temperature sensor 198 may be mounted onto a surface of hybrid board196. Temperature sensor 198 may also be an IR temperature sensororiented in a specific manner to detect infrared radiation emitted froma desired location of housing 192 (e.g., portion 200). Portion 200 mayemit IR energy 202 that is detected by temperature sensor 198.Temperature sensor 198 may then output a signal that changes based onthe changes to the IR energy 202 emitted from portion 200.

Although temperature sensor 198 is oriented to sense the temperature ofportion 200 of housing 192, temperature sensor 198 may instead beoriented to sense the temperature of primary coil 194 or some otherportion of the device. In any case, temperature sensor 198 may sense thetemperature of charging head 190 during a charging session to identifythe heat being applied adjacent to a patient's skin. In other examples,charging head 190 may include multiple temperature sensors, heat pipes,light pipes, or any other technique described herein (e.g., phosphorthermometry).

FIG. 9 is a conceptual cross-sectional diagram illustrating exampletemperature sensor 220 configured to detect the temperature of phasechange material 222 disposed within an IMD 210. IMD 210 may be similarto IMD 70 of FIG. 4A. However, IMD 210 may include phase change material222 disposed within housing 212. As shown in FIG. 9, IMD 210 includeshousing 212 that encloses hybrid board 214, electronics 216 and 218, andtemperature sensor 220. Hybrid board 214 may be mounted or securedwithin housing 22. Electronics 216 and 218 may include variouscomponents such as a processor and memory. Although not shown in FIG. 9,a secondary coil and rechargeable power source may also be disposedwithin housing 212. Temperature sensor 220 may be mounted onto a surfaceof hybrid board 214.

Temperature sensor 220 may be an infrared temperature sensor oriented ina specific manner to detect infrared radiation emitted from a desiredlocation of housing 212. Portion 224 may be an area of phase changematerial 222, adjacent to temperature sensor 220, from which thetemperature is to be sensed. As described herein, portion 224 may emitIR energy 226 as a function of the temperature of portion 224. Thetemperature of phase change material 222 may by a function of thetemperature of housing 212 when phase change material 222 is thermallycoupled to housing 212. As IR energy 226 is emitted from portion 224,temperature sensor 220 may detect at least some of IR energy 226 andoutput a signal representative of the intensity of IR energy 226.

Phase change material 222 may be provided for several reasons. Forexample, phase change material 222 may absorb heat generated in IMD 210during the charging session. Phase change material 222 may changebetween solid and liquid phases to absorb heat without increasing thetemperature of IMD 210. In addition, phase change material 222 maydisperse heat from various locations of IMD 210 to reduce temperaturevariations of housing 212. Therefore, the temperature sensed bytemperature sensor 220 may be representative of a larger surface area ofhousing 212.

Furthermore, phase change material 222 may be selected such that themelting point of phase change material 222 is a temperature above whichpower levels for the charging session may be decreased. In other words,a processor may track changes in temperature to identify when phasechange material 222 has fully changed phase and the temperature of IMD210 may be approaching undesirable levels. The temperature curve may bemonitored for inflection points that indicate energy is increasingtemperature instead of changing phase of phase change material 222, forexample. This temperature monitoring may eliminate the need forcalibration of temperature sensor 220 and/or avoid inaccuratemeasurements in temperature.

When a charging session first begins, the temperature of IMD 210 andphase change material 222 may increase. When phase change material 222begins to change phase, the sensed temperature from portion 224 mayremain at a relatively constant temperature during the charging sessionsubstantially throughout the phase change. Once phase change material222 has completely changed phase, the sensed temperature from portion224 may again begin to rise. At this second inflection point in thesensed temperature, a processor may determine that the power level forcharging may be decreased or even terminated to prevent additionalincreases in the temperature of housing 212. Since the sensedtemperatures are dependent upon known properties of phase changematerial 222, the output from temperature sensor 220 may not need to becalibrated during use of IMD 210. Changes to the detection circuitry oftemperature sensor 220 and/or electrical drift during measurement maynot affect the temperature readings. Instead, the processor may merelymonitor changes to the output signal from temperature sensor 220.

In another example, phase change material 222 may be used to calibratetemperature sensor 220 when IMD 210 is implanted within patient 12.Since the melting point or temperature at which phase change material222 changes phase is known, the output from temperature sensor 220 maybe calibrated based on when phase change material 222 changes phases.IMD 210 or charging device 22 may perform this calibration during eachrecharge session, after a predetermined number of recharging sessions,or according to a predetermined amount of time since the lastcalibration (e.g., a day, week, month, or year).

Phase change material 222 may be any compound or substance selected tochange phases (e.g., change from a solid state to a liquid state) at atemperature within the operating temperatures of IMD 210 or the devicewithin which phase change material 222 is used. Generally, the meltingpoint of the phase change material may be lower than a temperature thatwould be uncomfortable to patient 12. For example, the phase changematerial may be selected to have a melting point between approximately15 degrees Celsius and 50 degrees Celsius. More specifically, the phasechange material may have a melting point between approximately 25degrees Celsius and 45 degrees Celsius. In another example, the phasechange material may have a melting point between approximately 35degrees Celsius and 43 degrees Celsius.

Phase change material 222 may be selected from any variety of materialshaving properties sufficient to perform the functions described herein.For example, the phase change material may be a paraffin wax, a fattyacid, ester (carboxylic acid), inorganic materials such as salt hydratesor sodium hydrogen phosphate, or other compounds. The paraffin wax maybe a saturated alkane having between 19 and 23 carbon atoms that haveapproximate melting points in a desired range. Example paraffin waxesmay include nonadecane (C₁₉H₄₀; approximate melting point of 32.0degrees Celsius), eicosane or N-eicosane (C₂₀H₄₂; approximate meltingpoint of 36.4 degrees Celsius), heneicosane (C₂₁H₄₄; approximate meltingpoint of 40.4 degrees Celsius), docosane (C₂₂H₄₆; approximate meltingpoint of 44.4 degrees Celsius), or tricosane (C₂₃H₄₈; approximatemelting point of 47.4 degrees Celsius). In one example, the phase changematerial selected for energy transfer device 26 may include eicosane. Insome examples, the phase change material may include both eicosane andheneicosane

The amount of phase change material included within energy transferdevice 26 may be selected based on the power transferred by energytransfer device 26, the volume of IMD 210, the time needed for acharging session, and/or the desired temperature limit for IMD 210. Themass of phase change material 222 may also be based on the type ofmaterial selected. In some examples, IMD 210 may include betweenapproximately 1.0 gram of phase change material and 100 grams of phasechange material. However, more or less phase change material may be usedin other examples.

As described herein, phase change material 222 and temperature sensor220 may alternatively be disposed within charging head 26. When chargingdevice 26 determines that phase change material 222 has exceeded atemperature threshold or the second inflection point in temperature hasbeen identified, charging device 22 may terminate charging or instructthe user to terminate charging. In some examples, charging head 26 maybe configured to be thermally coupled to phase change materialcartridges that are replaceable by the user. Therefore, charging device22 may present an instruction to the user to replace the heatedcartridge with a new cartridge when the temperature exceeds a thresholdor the temperature begins to rise again once the material has completelychanged phase. This phase change material cartridge may allow the userto continue a charging session for longer durations.

FIG. 10 is a graph 230 of example temperatures generated in a patientduring IMD recharging over a period of time using a phase changematerial cartridge exchange. As shown in FIG. 10, graph 230 includestemperature 232 over time during recharging of rechargeable power source18. This temperature may be sensed with a non-thermally coupledtemperature sensor within charging head 26, for example. Therefore,temperature 232 may be representative of the temperature to which skincontacting charging head 26 may be subjected.

Graph 230 may indicate how temperature 232 changes when charging device22 charges rechargeable power source 18 during a charging session. Oncecharging of rechargeable power source 18 begins at the zero minute mark(start period 240), temperature 232 begins to increase fromapproximately 37 degrees Celsius. Charging device 22 may transmit powerto rechargeable power source 18 such that the temperature 232 rises at atemperature change rate 234. Once the phase change material of thecartridge begins to change phase (e.g., change from a solid to aliquid), the temperature change rate may decrease to temperature changerate 236B. The area of the curve between temperature change rates 235and 237 may be identified as inflection point 236A.

Once the phase change material completely changes phases from the solidto the liquid phase, temperature 232 may again increase. Inflectionpoint 236B identifies this increase to the temperature change rate. Oncecharging device 22 identified inflection point 236B, charging device 22may present a notification to the user to replace the phase changematerial cartridge. After the user replaces the phase change materialcartridge at cartridge change 242 (e.g., at approximately 35 minutesinto the charging session), temperature 232 may begin to decrease as thenew cartridge acts as a heat sink for the heat of charging head 26.Charging device 22 may detect subsequent increases to the temperaturechange rate and again present a notification to the user to change thephase change material cartridge.

If the user does not change the phase change material cartridge,temperature 232 may continue to increase along temperature curve 238.Charging device 22 may continue to monitor the sensed temperature andreduce the power level of charging or terminate charging if temperature232 exceeds a temperature threshold. In this manner, charging device 22may provide a safety override for charging if the user fails to changethe phase change material cartridge.

Temperature 232 of graph 230 is only an example of tissue temperaturechanges due to charging rechargeable power source 18. In the example ofFIG. 10, temperature 230 may increase to approximately 40.5 degreesCelsius prior to presenting the cartridge change notification to theuser. In other examples, temperature 232 may change at faster or slowerrates. In addition, temperature 232 may plateau at lower temperatures,plateau at higher temperatures, or not plateau at all during therecharge session. In some examples, temperature 232 may reachtemperatures in excess of 42 degrees Celsius or even 43 degrees Celsius.

Temperature 232 of graph 230 may also apply to temperatures in otherdevices used to charge rechargeable power source 18. For example, IMD210 may be subject to similar temperatures during charging. In addition,a processor may similarly identify inflection point 236B in IMD 210 toadjust the power level during charging or terminate charging asdescribed with respect to FIG. 9. In other examples, exampletemperatures of graph 230 may also apply to devices without a phasechange material.

FIG. 11 is a flow diagram that illustrates an example technique forcontrolling the charging of implantable rechargeable power source 18based on a sensed temperature. Although processor 50 of charging device22 will be described as generally performing the technique of FIG. 11,the technique of FIG. 11 may instead be performed by a combination ofprocessors 30 and 50, in other examples. The technique of FIG. 11 may beapplied to temperatures sensed by non-thermally coupled temperaturesensors disposed within implantable device and/or external devices(e.g., external charging device 22 or charging head 26) associated withcharging an implanted medical device.

A charging session for rechargeable power source 18 may begin whenprocessor 50 receives a charge request via user interface 54 (250).Processor 50 may select the power level for charging (e.g., a high powerlevel) (252). Processor 50 may then control charging device 22 to chargepower source 18 with the selected power level (254). During charging,temperature sensor 39 may sense the temperature of a portion of IMD 14using non-thermal coupling (e.g., non-contact) techniques describedherein (256). Processor 30 may transmit the sensed temperatures tocharging device 22 via telemetry modules 36 and 56. As long as thesensed temperature remains below or equal to the threshold (“NO” branchof block 258), processor 50 may continue to charge power source 18 withthe high power level (254).

In response to the sensed temperature becoming greater than thethreshold (“YES” branch of block 258), processor 50 may determine ifcharging is to stop (260). For example, processor 50 may have received astop charging command from the user, power source 18 may be fullyrecharged, or the charging session may be stopped for any other reason.If processor 50 is not to stop charging (“NO” branch of block 260),processor 50 may select a lower power level (262) and continue to chargepower source 18 (256). This lower level may be a trickle charge, acycled (on/off) charge or other power level that does not increase thetemperature of charging head 26 or IMD 14 above a desired temperaturethreshold. If processor 50 determines that the charging session is to bestopped (“YES” branch of block 260), processor 50 may terminate thecharging session (264).

In this manner, processor 50 may control the charging of rechargeablepower source 18 based on the sensed temperatures from one or morenon-thermally coupled temperature sensor. In the case of multipletemperatures, processor 50 may control the charging based on thetemperature sensor outputting the highest temperatures. In otherexamples, processor 50 may average or otherwise generate an overalltemperature based on the multiple temperature measurements.

FIG. 12 is a flow diagram that illustrates an example technique forpresenting a notification to a user for exchanging a phase changematerial cartridge. Processor 50 of charging device 22 will be describedas generally performing the technique of FIG. 12. However, otherprocessors or devices may contribute to the technique of FIG. 12. Thetechnique of FIG. 11 may be applied to temperatures sensed bynon-thermally coupled temperature sensors disposed within chargingdevice 22, charging head 26, or any other device that may include areplaceable heat sink.

Processor 50 may begin charging rechargeable power source 18 in responseto receiving a command from a user or other received instructions (270).Using a non-thermally coupled temperature sensor within charging head 26(e.g., temperature sensor 198 of IMD 190), processor 50 may sense thetemperature of charging head 26 associated with the charging session(272). Processor 50 may then calculate a temperature change rate fromthe sensed temperatures (274). Processor 50 may also compare the sensedtemperature to a threshold (276). If the sensed temperature exceeds athreshold (“YES” branch of block 276), processor 50 may terminate thecharging session (286). The threshold may be used as a safety for whenthe user fails to replace the phase change material cartridge.

If the sensed temperature is less than or equal to the threshold (“NO”branch of block 276), processor 50 may determine if there has been asecond temperature change rate change such as an inflection point in thesensed temperature (278). The first temperature change rate adjustment,or inflection point, may be due to the phase change material changingphase without increasing in temperature. The second temperature changerate change, or inflection point, may be due to the phase changematerial having fully changed from a solid phase to a liquid phase. Ifprocessor 50 does not detect the second rate change (“NO” branch ofblock 278), processor 50 may continue to sense the temperature ofcharging head 26 (272).

In response to detecting the second rate change (“YES” branch of block278), processor may present a notification to the user to exchange orreplace the phase change material cartridge (280). The notification maybe a visual message, an audible alert, or even a tactile vibration. Inresponse to receiving a confirmation input from a user that confirms thecartridge has been changed (“YES” branch of block 282), processor 50 maycontinue sensing the temperature (272). If processor 50 has not receiveda confirmation input (“NO” branch of block 282), processor 50 maycompare the sensed temperature to a threshold such as the threshold inblock 276 (284). If the sensed temperature is less than or equal to thethreshold (“NO” branch of block 284), processor 50 may continue topresent the notification (280) and wait for the confirmation input. Inresponse to determining that the sensed temperature has exceeded thethreshold (“YES” branch of block 284), processor 50 may terminate thecharging session (286).

FIG. 13 is a flow diagram that illustrates an example technique fordetecting a fault condition of a medical device component. Processor 30of IMD 14 will be described as generally performing the technique ofFIG. 13. However, other processors or devices (e.g., processor 50 ofexternal charging device 22) may contribute to or separately perform thetechnique of FIG. 13.

Processor 30 may receive an instruction to sense temperature for faultcondition detection of one or more circuits within IMD 14 (290).Processor 30 may then instruct temperature sensor 39 to measure thetemperature of a target component (292). The target component may be aportion of an electrical circuit, a component coupled to a circuit(e.g., power source 18), or a surface of the housing that houses one ormore electrical circuits that may be subject to a fault condition.

The fault condition may be indicative of excess current present withinone or more electrical circuits of IMD 14. These electrical circuits mayinclude processor 30, temperature sensor 39, and or other componentsthat perform one or more functions for IMD 14. Excess current, e.g., afault condition, may increase the temperature of one or more componentswithin IMD 14 and potentially damage an electrical circuit or otherelectrical coupled component. Although the temperature may be sensed forthe specific purpose of monitoring and detecting a possible faultcondition, the temperature may instead be a sensed temperature measuredfor any general purpose.

Processor 30 may then compare the sensed temperature to a faultcondition threshold (294). If the sensed temperature is less than thefault condition threshold (“NO” branch of block 294), processor 30 maywait until the next instruction to sense the temperature for faultcondition detection (290). If the sensed temperature is greater than orequal to, or otherwise exceeds, the fault condition threshold (“YES”branch of block 294), processor 30 may determine if rechargeable powersource 18 is being charged (296). The fault condition threshold may be astored temperature (e.g., approximately 43 degrees Celsius) that mayindicate a fault has occurred within an electrical circuit that isproducing excess current and resulting in increased temperatures. Inother examples, the fault condition threshold may be a representation ofthe temperature over time. For example, the fault condition thresholdmay be a rate of temperature change, a magnitude of temperature changeover a predetermined period of time, or other equations representativeof how the temperature has changed. Temperature change over time may beindicative of a fault condition instead of another condition duringoperation of IMD 14. For example, quickly rising temperatures may bemore indicative of a fault condition than slower rising temperaturesassociated with recharging power source 18.

If a charging session is occurring to charge power source 18 (“YES”branch of block 296), processor 30 may terminate the recharge session(298). Processor 30 may terminate the recharge session by transmitting atermination request to external charging device 22. Alternatively,processor 30 may open a switch between coil 40 and power source 18 thatprevents further charging of power source 18. Processor 30 may thendisconnect power source 18 from at least one electrical circuit of IMD14 (300). If no charging session is currently occurring (“NO” branch ofblock 296), processor may disconnect power source 18 from at least oneelectrical circuit of IMD 14 (300). Disconnection of power source 18 mayimmediately reduce temperatures of IMD 14 by reducing or terminatingcurrent flow within IMD 14. Processor 30 may disconnect power source 18from the at last one electrical circuit by opening a switch betweenpower source 18 and the at least one electrical circuit. In someexamples, processor 30 may or may not be included in an electricalcircuit disconnected from power source 18.

Processor 30 may periodically check for a fault condition using thesensed temperature from temperature sensor 39. In some examples,processor 30 may perform the fault detection process prior to starting arecharge session. If the sensed temperature is greater than the faultcondition threshold, processor 30 may instruct charging device 22 towithhold any power transmission for recharging power source 18. In otherexamples, processor may detect a severity of the fault condition (e.g.,the magnitude of the excess current within IMD 14). If the faultcondition is minimal, processor 30 may limit certain functions toprevent the fault condition from raising temperatures or damaging anycircuits. A minimal fault condition may also trigger processor 30 tolimit the current used to charge power source 18 and/or command chargingdevice 22 to limit the power level used to charge power source 18. Inaddition to sensing temperature to detect a fault condition, processor30 may monitor current values within one or more electrical circuitsthat may indicate a fault condition. In this manner, processor 30 mayhave redundant or backup sensing methods to ensure detection of a faultcondition or confirm that a fault condition has occurred.

In other examples, processor 30 may utilize two or more temperaturesensors to sense the temperature of different surfaces within IMD 14.For example, processor 30 may measure the temperature at multipleportions of the housing. Processor 30 may compare one or more of themeasured temperatures to respective fault condition thresholds (or asingle threshold) and determine which of the temperatures exceed therespective threshold. Based on which temperature(s) exceeds thethreshold, processor 30 may identify or estimate which component withinIMD 14 is responsible for creating the fault condition. Processor 30 mayreduce the functionality of this component, reduce the current to thiscomponent, shut down the component, or otherwise selectively alterelectrical currents within the electrical circuitry to remedy the faultcondition of the identified component.

FIG. 14 is a flow diagram that illustrates an example technique forcalibrating a non-thermally coupled temperature sensor. The process ofFIG. 14 will be described with respect to manufacturing IMD 14 withinnon-thermally coupled temperature sensor 39. However, this calibrationprocess may additionally or alternatively be performed by processor 30of IMD 14 or processor 50 of external charging device 22 duringoperation of the device using a non-thermally coupled temperature sensor(e.g., temperature sensors 39 and/or 59) described herein. For example,a shutter may be a black body that moves over the temperature sensorwithin the device.

When manufacturing IMD 14, temperature sensor 39 may be calibrated suchthat the output signal from temperature sensor 39 is mapped to thetemperature sensed by temperature sensor 39 when the output signal wasproduced. A calibration machine or a user may position a “black body” infront of the temperature sensor 39 to be calibrated (302). The blackbody may be a material that emits infrared radiation at a rate andmagnitude independent of the temperature of the material. In otherwords, the emissivity of the black body may be relatively constantindependent of ambient temperature. Although the emissivity may changedue to large variations in temperature, the emissivity may remainrelatively constant over the temperature ranges to which IMD 14 isnormally subjected (e.g., 20 degrees Celsius to 43 degrees Celsius). Inthis manner, temperature sensor 39 may be calibrated without maintaininga specific ambient temperature within which temperature sensor 39 andthe black body must be calibrated.

Once the black body is placed within sensing range of temperature sensor39, temperature sensor 39 may be controlled to sense the infraredradiation from the black body (304). A processor (e.g., processor 30 ora processor of an external device) may receive the output signal fromtemperature sensor 39 (306). The processor may then calibrate the outputof temperature sensor 39 to the known temperature of the emissivity ofthe black body (308). For example, if the infrared emissivity of theblack body represents a temperature of 37 degrees Celsius of the surfacefrom which temperature sensor 39 will be sensing within IMD 14, theoutput of temperature sensor 39 may be calibrated to represent 37degrees Celsius. This calibration process may be repeated with one ormore black bodies of with different emissivities to create a calibrationcurve for temperature sensor 39 in some examples.

In some examples, the calibration of temperature sensor 39 may, but neednot, be performed for each sensor being manufactured or for each medicaldevice being manufactured. Since infrared temperature sensors may haveminimal part-to-part variation, the output from one temperature sensorto another temperature sensor may be relatively equal. Therefore, thecalibration process may only need to be performed for a batch oftemperature sensors or even once during design of the temperaturesensor. In this case, a universal calibration may be performed using onetemperature sensor, and the universal calibration may be applied to allof the temperature sensors manufactured equivalently.

In other examples, a temperature sensor within the IMD (e.g.,temperature sensor 39 in IMD 14) may be calibrated using a calibratedtemperature sensor within an external device. For example, externalcharging device 22 may include a temperature sensor that is calibrated.When external charging device 22 is placed in contact with patient 12and proximate to IMD 14, IMD 14 may utilize the sensed temperature fromthe calibrated temperature sensor to calibrate temperature sensor 39.Alternatively, charging device 22 may calibrate the output oftemperature sensor 39 received from IMD 14.

In still another example, one or more temperature sensors may becalibrated during a first recharge session by monitoring a deflectionpoint in the temperature curve associated with temperature of a phasechange material as discussed above. This deflection point (e.g., pointat which temperature plateau ceases and temperature rises followingcompletion of phase change) may be associated with a known absolutetemperature that may be used to calibrate one or more temperaturesensors. Once this calibration is performed, charging device 22 may thenbegin the charging session.

Alternatively, non-thermally coupled temperature sensors may not need tobe calibrated. Instead, a pair of temperature sensors may be utilizedand common mode rejection used to determine a temperature differenceinstead of an absolute temperature value. In another example, atemperature difference from one sensor may be used instead of acalibrated absolute temperature. Since the temperature before a chargingsession may be approximately equal to normal body temperature, thesystem may use the relative change in temperature to determine how tocontrol charging of IMD 14.

According to the techniques and devices described herein, an IMD orexternal charging device may include one or more temperature sensors(e.g., an IR sensor, phosphor temperature sensor, or any other sensornot requiring thermal coupling to determine temperature) configured tosense the temperature of a portion of the device not thermally coupledto the temperature sensor. These non-thermally coupled sensors may bemounted on a PCB or hybrid board and directed toward a specific surfaceto be sensed. In this manner, non-thermally coupled sensors may obtaintemperature information about one or more portions of the device withoutbeing physically coupled to the portion of interest. The IMD and/orexternal charging device may then control charging of an implantablerechargeable power source using the sensed temperatures.

This disclosure is primarily directed to wireless transfer of energybetween two coils (e.g., inductive coupling). However, one or moreaspects of this disclosure may also be applicable to energy transferinvolving a physical connection between a charging device and arechargeable power supply. For example, aspects of this disclosure maybe applicable to charging the power supply of an IMD by inserting aneedle coupled to an external charging device through the skin and intoa port of the IMD. Although physical connections for energy transfer maynot introduce heat losses due to energy transfer between wireless coils,heat may still be generated and lost to the patient from componentswithin the IMD (e.g., the battery being charged and circuits involved inthe recharging of the power supply).

The disclosure also contemplates computer-readable storage mediacomprising instructions to cause a processor to perform any of thefunctions and techniques described herein. The computer-readable storagemedia may take the form of any volatile, non-volatile, magnetic,optical, or electrical media, such as a RAM, ROM, NVRAM, EEPROM, flashmemory, or any other digital media. The computer-readable storage mediamay be non-transitory in that the storage media is not anelectromagnetic carrier wave. However, this does not mean that thestorage media is not transportable or that it non-volatile. Aprogrammer, such as patient programmer or clinician programmer, may alsocontain a more portable removable memory type to enable easy datatransfer or offline data analysis.

The techniques described in this disclosure, including those attributedto IMD 14, charging device 22, or various constituent components, may beimplemented, at least in part, in hardware, software, firmware or anycombination thereof. For example, various aspects of the techniques maybe implemented within one or more processors, including one or moremicroprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated,discrete, or analog logic circuitry, as well as any combinations of suchcomponents, embodied in programmers, such as physician or patientprogrammers, stimulators, image processing devices or other devices. Theterm “processor” or “processing circuitry” may generally refer to any ofthe foregoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry.

Such hardware, software, firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. While the techniques describedherein are primarily described as being performed by processor 30 of IMD14, processor 50 of charging device 22, or any one or more parts of thetechniques described herein may be implemented by a processor of one ofIMD 14, charging device 22, or another computing device, alone or incombination with each other.

In addition, any of the described units, modules or components may beimplemented together or separately as discrete but interoperable logicdevices. Depiction of different features as modules or units is intendedto highlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method comprising: sensing a temperature of aportion of a housing of a medical device by a temperature sensordisposed within the housing of the medical device, wherein thetemperature sensor is configured to sense the temperature of the portionof the housing without being thermally coupled to the portion of thehousing; determining, based on the sensed temperature, that a faultoccurred with a component of the medical device; and responsive todetermining that the fault occurred, controlling an operation associatedwith the medical device.
 2. The method of claim 1, wherein controllingthe operation associated with the medical device comprises controllingan external charging device to limit a power level of current generatedby the external charging device that charges a rechargeable power sourceof the medical device.
 3. The method of claim 2, wherein controlling theexternal charging device to limit the power level comprises controllingthe external charging device to withhold power transmission to therechargeable power source.
 4. The method of claim 1, wherein controllingthe operation associated with the medical device comprises limiting afunctionality of one or more components of the medical device to preventthe temperature of the medical device from further rising due to thefault condition.
 5. The method of claim 1, wherein controlling theoperation associated with the medical device comprises reducing anelectrical current delivered to a component identified as causing thefault.
 6. The method of claim 1, wherein determining that the faultoccurred comprises determining that the sensed temperature exceeds afault condition threshold.
 7. The method of claim 1, wherein determiningthat the fault occurred comprises determining that a rate of change ofthe sensed temperature exceeds a fault condition threshold rate oftemperature change.
 8. The method of claim 1, wherein determining thatthe fault occurred comprises determining that a magnitude of change ofthe sensed temperature over a predetermined period of time exceeds afault condition threshold magnitude of temperature change over thepredetermined period of time.
 9. The method of claim 1, wherein sensingthe temperature of the portion of the housing comprises sensing a firsttemperature of a first portion of the housing with a first temperaturesensor, and wherein the method further comprises: sensing a secondtemperature of a second portion of the housing with a second temperaturesensor; determining that at least one of the sensed first temperature orthe sensed second temperature exceeds a fault threshold; identifying,based on the at least one of the sensed first temperature or the sensedsecond temperature exceeds the fault threshold, a component of themedical device responsible for creating the fault, wherein controllingthe operation associated with the medical device comprises controllingoperation of the component to address the fault.
 10. The method of claim1, wherein sensing the temperature comprises sensing the temperaturewith the temperature sensor being mounted to a printed circuit boardwithin the housing of the medical device.
 11. A system comprising: amedical device comprising a housing; a temperature sensor disposedwithin the housing of the medical device and configured to sense atemperature of a portion of the housing of the medical device, whereinthe temperature sensor is configured to sense the temperature withoutbeing thermally coupled to the portion of the housing; and processingcircuitry configured to: determine, based on the sensed temperature,that a fault occurred with a component of the medical device; andresponsive to the determination that the fault occurred, control anoperation associated with the medical device.
 12. The system of claim11, wherein the processing circuitry is configured to control theoperation associated with the medical device by controlling an externalcharging device to limit a power level of current generated by theexternal charging device that charges a rechargeable power source of themedical device.
 13. The system of claim 12, wherein the processingcircuitry is configured to control the operation associated with themedical device by controlling the external charging device to withholdpower transmission to the rechargeable power source.
 14. The system ofclaim 11, wherein the processing circuitry is configured to control theoperation associated with the medical device by limiting a functionalityof one or more components of the medical device to prevent thetemperature of the medical device from rising due to the faultcondition.
 15. The system of claim 11, wherein the processing circuitryis configured to control the operation associated with the medicaldevice by reducing an electrical current delivered to a componentidentified as causing the fault.
 16. The system of claim 11, wherein theprocessing circuitry is configured to determine that the fault occurredby determining that the sensed temperature exceeds a fault conditionthreshold.
 17. The system of claim 16, wherein the processing circuitryis configured to determine that the fault occurred by determining that arate of change of the sensed temperature exceeds a fault conditionthreshold rate of temperature change.
 18. The system of claim 16,wherein the processing circuitry is configured to determine that thefault occurred by determining that a magnitude of change of the sensedtemperature over a predetermined period of time exceeds a faultcondition threshold magnitude of temperature change over thepredetermined period of time.
 19. The system of claim 11, wherein: thetemperature is a first temperature, the portion of the housing is afirst portion of the housing, and the temperature sensor is a firsttemperature sensor, the system further comprises a second temperaturesensor configured to sense second temperature of a second portion of thehousing, and the processing circuitry is configured to: determine thatat least one of the sensed first temperature or the sensed secondtemperature exceeds a fault threshold; identify, based on the at leastone of the sensed first temperature or the sensed second temperatureexceeds the fault threshold, a component of the medical deviceresponsible for creating the fault; and control the operation associatedwith the medical device by controlling operation of the component toaddress the fault.
 20. The system of claim 11, further comprising aprinted circuit board within the housing of the device, wherein thetemperature sensor is mounted to the printed circuit board.
 21. Thesystem of claim 11, wherein the medical device comprises an implantablemedical device that houses a stimulation generator and a rechargeablepower source.
 22. A system comprising: means for sensing a temperatureof a portion of a housing of a medical device without being thermallycoupled to the portion of the housing, the means for sensing thetemperature being disposed within the housing of the medical device;means for determining, based on the sensed temperature, that a faultoccurred with a component of the medical device; and means for,responsive to determining that the fault occurred, controlling anoperation associated with the medical device.